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#pragma GCC optimize("O3")
#include "bits/stdc++.h"
using namespace std;
#define rep(i,a,b) for(int i=(a); i<(b); ++i)
#define all(x) x.begin(),x.end()
#define sz(x) int(x.size())
typedef long long ll;
typedef unsigned long long ull;
typedef vector<int> vi;
typedef vector<vi> vvi;

const int oo = 1e9;

void cmax(int& a, int b){
    a = max(a,b);
}

const int N = 8010;
int dp[N][N][2];

int main(){
    cin.tie(NULL),cin.sync_with_stdio(false);
    
    int n,k,t; cin >> n >> k >> t;

    string s; cin >> s;

    vi pref(n+1);
    rep(i,0,n) pref[i+1] = pref[i] + (s[i] != '3');

    rep(i,0,n+1) rep(j,0,k+1) rep(l,0,2) dp[i][j][l] = -oo;
    dp[0][0][0] = 0;

    rep(i,0,n){
        rep(j,0,k+1){
            // stay at home
            int to = j + (s[i] != '3');
            if (to <= k)
                cmax(dp[i+1][to][0], dp[i][j][0] + 1);
            to = j + (s[i] == '1');
            if (to <= k) cmax(dp[i+1][to][0], dp[i][j][0]);

            // go to work or come home
            if (i+1>=t){
                int need = pref[i+1] - pref[i+1-t];
                if (need + j <= k){
                    cmax(dp[i+1][need + j][1], dp[i+1-t][j][0]);
                    cmax(dp[i+1][need + j][0], dp[i+1-t][j][1]);
                }
            }

            // stay at work
            cmax(dp[i+1][j][1],dp[i][j][1]);
        }
    }

    int ans = -oo;
    rep(miss,0,k+1) cmax(ans, dp[n][miss][0]);

    if (ans < 0){
        cout << "-1\n";
    }else{
        cout << ans << '\n';
    }
}