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/* -----------------------
Autor: Tomasz Boguslawski
-------------------------- */
#include<cstdio>
#include<cstdlib>
#include<iostream>
#include<fstream>
#include<iomanip>
#include<string>
#include<sstream>
#include<cstring>
#include<map>
#include<vector>
#include<set>
#include<queue>
#include<algorithm>
#include <fstream>
#include<math.h>

#define LL long long
#define FOR(x, b, e) for(LL x = b; x <= (e); x++)
#define FORS(x, b, e, s) for(LL x = b; x <= (e); x+=s)
#define FORD(x, b, e) for(LL x = b; x >= (e); x--)
#define VAR(v, n) __typeof(n) v = (n)
#define ALL(c) (c).begin(), (c).end()
#define FOREACH(i, c) for(VAR(i, (c).begin()); i != (c).end(); ++i)
#define DEBUG if (debug)
#define MIN(a,b) ((a>b)?b:a)
#define MAX(a,b) ((a>b)?a:b)

using namespace std;

const LL M=998244353;

set<string> subwords;
set<string> subwords2;

void recurse(string &s, LL pos, string sub)
{
    string z = s[pos]+sub;
    if (subwords.count(z)>0) subwords2.insert(z);
    else subwords.insert(z);
    if (pos!=0)
    {
        recurse(s, pos-1, z);
        recurse(s, pos-1, sub);
    }
}

LL brut(string s)
{
    subwords.clear(); subwords2.clear();
    recurse(s, s.size()-1, "");
    FOREACH(p,subwords2) cout << *p << "\n";
    cout << "Subwords: " << subwords.size() << "\n";
    cout << "Subwords repeated: " << subwords2.size() << "\n";
    cout << "Singletons: " << (subwords.size()-subwords2.size()) << "\n";
    return subwords2.size();
}

LL dp[1000];
LL last[1000];

LL calc(string s)
{
    LL len=s.size();
    FOR(i,0,999) last[i]=-1;

    FOR(i,0,len-1)
    {
        cout << "i=" << i << " s[i]=" << s[i] << " last[s[i]]=" << last[s[i]] << "\n";
        if (i==0) dp[i]=2; else dp[i]=2*dp[i-1];
        if (last[s[i]]>0)
        {
            dp[i] -= dp[last[s[i]]-1];
            cout << " odejmuje: " << dp[last[s[i]]-1] << "\n";
        }
        last[s[i]]=i;
    }
    return dp[len-1] - 1;
}

int countSub(string str)
{
    // Create an array to store index
    // of last
    vector<int> last(256, -1);

    // Length of input string
    int n = str.length();

    // dp[i] is going to store count of distinct
    // subsequences of length i.
    int dp[n + 1];
    int db[n + 1];

    // Empty substring has only one subsequence
    dp[0] = 1;
    db[0] = 0;

    // Traverse through all lengths from 1 to n.
    for (int i = 1; i <= n; i++) {
        // Number of subsequences with substring
        // str[0..i-1]
        dp[i] = 2 * dp[i - 1];
        db[i] = 2 * db[i - 1];
        cout << "character=" << str[i-1] << " last=" << last[str[i-1]] << "\n";
        // If current character has appeared
        // before, then remove all subsequences
        // ending with previous occurrence.
        if (last[str[i - 1]] != -1)
        {
            dp[i] = dp[i] - dp[last[str[i - 1]]];
            cout << "odjete: " << dp[last[str[i - 1]]] << "\n";
            db[i] += dp[last[str[i - 1]]] - 2*db[last[str[i-1]]+1];
        }

        // Mark occurrence of current character
        last[str[i - 1]] = (i - 1);
        cout << "dp[" << i << "]=" << dp[i] << "\n";
    }

    //return dp[n];
    return db[n];
}

LL g[60000];
LL subs[60000];

class Node
{
public:
    LL pocz, kon;
    LL value;
    Node* parent;
    Node* child1; Node* child2;
    Node() { parent=NULL; child1=NULL; child2=NULL; value=0; }
    void addValue(LL delta)
    {
        value=(value+delta)%M;
        if (value<M) value+=M;
        if (parent!=NULL) parent->addValue(delta);
    }
    void setValue(LL newValue)
    {
        LL delta=newValue-value;
        if (delta<0) delta+=M;
        this->addValue(delta);
    }
    LL getSum(LL p, LL k)
    {
        if (p<=pocz&&k>=kon) return value;
        if (p>kon||k<pocz) return 0;
        return (child1->getSum(p,k)+child2->getSum(p,k))%M;
    }
};

Node* nodes[600000];
Node* root;

Node* createTree(LL pocz, LL kon, Node* parent)
{
    //cout << "Creating node: " << pocz << ".." << kon << "\n";
    Node* node=new Node();
    node->parent=parent;
    node->pocz=pocz; node->kon=kon;
    node->value=0;
    if (pocz==kon) nodes[pocz]=node;
    else
    {
        LL mySize=kon-pocz+1;
        LL half = mySize/2;
        node->child1 = createTree(pocz, pocz+half-1, node);
        node->child2 = createTree(pocz+half, kon, node);
    }
    return node;
}

LL antiSingletons(string &s)
{
    LL n = s.size()-1;
    //s = '#'+s;

    LL last[256]; FOR(i,0,255) last[i]=-1;
    g[0]=1; // jeden singleton dlugosci 0 (?)
    subs[0]=1;
    LL sum=1;
    FOR(i,1,n)
    {
        char t = s[i];
        //cout << "-- pos: " << i << " char: " << t << "\n";
        subs[i]=(2*subs[i-1])%M;
        LL lastPos = last[t];
        if (lastPos!=-1)
        {
            //cout << " lastPos=" << lastPos << " g[lastPos]=" << g[lastPos] << "\n";
            //LL sum2=0;
            //FOR(j,lastPos,i-1) sum2+=g[j];
            LL sum2=root->getSum(lastPos,i-1);
            sum2=sum2%M;
            sum -= g[lastPos]; // jesli byly jakies zakonczone na ostatnim t, to wypadaja
            if (sum<0) sum+=M;
            g[lastPos]=0; nodes[lastPos]->setValue(0);
            g[i]=sum2; nodes[i]->setValue(sum2);
            sum=(sum+g[i])%M;
            subs[i] -= subs[lastPos-1];
            if (subs[i]<0) subs[i]+=M;
        }
        else
        {
            //cout << " first timer\n";
            g[i] = sum; nodes[i]->setValue(sum);
            sum = (sum * 2)%M;
        }
        last[t]=i;
        //cout << " g[" << i << "]=" << g[i] << " sum=" << sum << "\n";
    }

    LL pp=subs[n]-sum; if (pp<0) pp+=M;
    //cout << "Subs=" << subs[n] << "\n";

    return pp;
}

/// MAIN
int main(int argc, char* argv[])
{
    // magic formula, which makes streams work faster:
	ios_base::sync_with_stdio(0);
    LL n; LL q; LL pos; char ch;
    cin >> n; cin >> q;
    LL ts=2; while (ts<n) ts*=2;
    //cout << "Tree size: " << ts << "\n"; cout.flush();
    root=createTree(1,ts,NULL);
    string s;
    cin >> s;
    s = '#'+s;
    cout << antiSingletons(s) << "\n";
    FOR(i,1,q)
    {
        cin >> pos; cin >> ch;
        s[pos]=ch;
        cout << antiSingletons(s) << "\n";
    }
	return 0;
}