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#include <bits/stdc++.h>
using namespace std;
typedef pair<int,int> PII;

int n, k, t;

int pref[3][8005];

int sum(int t, int l, int r) {
    return pref[t][r] - pref[t][l-1]; 
}

int res = -1;
inline void update_res(int pr, int zd, int fr, int mis) {
    if(pr + mis > k) return;
    if(zd + pr + mis < k) res = max(res, fr+zd+pr);
    else res = max(res, fr+k-mis);
}

int main() {
    ios_base::sync_with_stdio(0);
    cin>>n>>k>>t;
    for(int i=1;i<=n;i++) {
        char x;
        cin>>x;
        int a = x-'0'-1;
        pref[0][i] = pref[0][i-1];
        pref[1][i] = pref[1][i-1];
        pref[2][i] = pref[2][i-1];
        pref[a][i]++;
    }

    update_res(pref[0][n], pref[1][n], pref[2][n], 0);

    for(int i=1;i<=n-2*t+1;i++) {
        for(int j=i+t;j<=n-t+1;j++) {
            int pr = pref[0][i-1] + pref[0][n] - pref[0][j+t-1];
            int zd = pref[1][i-1] + pref[1][n] - pref[1][j+t-1];
            int fr = pref[2][i-1] + pref[2][n] - pref[2][j+t-1];
            int mis = sum(0, i, i+t-1) + sum(0, j, j+t-1) + sum(1, i, i+t-1) + sum(1, j, j+t-1);
            update_res(pr, zd, fr, mis);
            // cout<<i<<" "<<j<<" "<<pr<<" "<<zd<<" "<<fr<<" "<<mis<<" "<<res<<endl;
        }
    }

    cout<<res<<endl;
}