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#include <bits/stdc++.h>
using namespace std;
typedef long long int ll;

constexpr int N = 8000;
int pref[N+9][3];

int main(){
    ios_base::sync_with_stdio(0);
    cin.tie(0); cout.tie(0);
    int n,k,t;
    string a;
    cin >> n >> k >> t;
    cin >> a;
    for (int x=1;x<=n;x++){
        pref[x][0]=pref[x-1][0]; pref[x][1]=pref[x-1][1]; pref[x][2]=pref[x-1][2];
        pref[x][a[x-1]-'1']++;
    }
    k = pref[n][0]+pref[n][1]-k;
    int odp=-1;
    for (int x=t+1;x<=n;x++){
        for (int y=x;y<=n-t;y++){
            int biur = pref[y][0]-pref[x-1][0] + pref[y][1]-pref[x-1][1];
            int free = x-t + n-t-y-1;
            int zdal = pref[x-t][1] + pref[n][1]-pref[y+t][1];
            if (biur + zdal >= k){
                odp=max(odp,free-max(k-biur,0));
            }
        }
    }
    if (pref[n][1] >= k)odp=max(odp,n-max(k,0));
    cout << odp << '\n';
}