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#include <bits/stdc++.h>
#define ll long long
#define llu long long unsigned
#define ld long double
#define fr(i,n) for(int i=0;i<n;i++)
#define watch(x) cout<<(#x)<<"=="<<(x)<<endl
#define ft first
#define sc second
#define mp make_pair
#define pb push_back
#define vi vector<int>
#define pii pair<int,int>
#define P 1000000007llu
#define N 405
#define LC 262144
using namespace std;

int n,k,t;
string s;
set<int> ones,twos;

int main() {
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    cout.tie(NULL);
    cin>>n>>k>>t>>s;
    fr(i,n) if(s[i]=='1') {
        ones.insert(i);
    } else if(s[i]=='2') {
        twos.insert(i);
    }
    if(k>=ones.size()) {
        cout<<n-ones.size()-(twos.size()-max((size_t)0,(k-ones.size())))<<'\n';
        return 0;
    }
    fr(i,t) if(s[i]=='1'||s[i]=='2') k--;
    fr(i,t) if(s[n-1-i]=='1'||s[i]=='2') k--;
    if(k<0) cout<<"-1\n";
    else cout<<n-2*t-ones.size()-twos.size()+k;
    return 0;
}