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#pragma GCC optimize ("O3")
#include <bits/stdc++.h>
using namespace std;
#define int long long
#define rep(i, a, b) for (int i = (a); i <= (b); i++)
#define per(i, a, b) for (int i = (b); i >= (a); i--)
#define SZ(x) ((int)x.size())
#define all(x) x.begin(), x.end()
#define pb push_back
#define mp make_pair
#define st first
#define nd second
using ll = long long;
using lf = long double;
using pii = pair <int,int>;
using pll = pair<ll, ll>;
auto& operator<<(auto& o, pair<auto, auto> p) {
    return o << "(" << p.first << ", " << p.second << ")";
}
auto operator<<(auto& o, auto x)->decltype(end(x), o) {
    o << "{"; int i = 0; for (auto e: x) o << ", " + 2*!i++ << e;
    return o << "}";
}
#define dbg(x...) cerr<<"["#x"]: ", [](auto...$) {((cerr << $ << "; "),...)<<endl;}(x)
const int mxN = 8007;
int pref[4][mxN];

int32_t main(){
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    int n,k,t; cin >> n >> k >> t;
    string s; cin >> s;
    rep(i,0,n-1){
        rep(x,1,3) pref[x][i+1] = pref[x][i];
        pref[s[i]-'0'][i+1]++;
    }
    int res = -1;

    if(pref[3][n] <= k){
        int b = pref[1][n];
        int z = 0;
        int nb = pref[1][n];
        int nz = pref[2][n];
        int w = pref[3][n];
        res = max(res, w + nb + min(k-b-z, nz));

    }
    rep(i,1,n-t+1) rep(j,i+t,n-t+1){ //i-i+t-1, j-j+t-1
        int b = pref[1][i+t-1] - pref[1][i-1] + pref[1][j+t-1] - pref[1][j-1];
        int z = pref[2][i+t-1] - pref[2][i-1] + pref[2][j+t-1] - pref[2][j-1];
        int nb = pref[1][i-1] + pref[1][n] - pref[1][j+t-1];
        int nz = pref[2][i-1] + pref[2][n] - pref[2][j+t-1];
        int w = pref[3][i-1] + pref[3][n] - pref[3][j+t-1];
        if(b+nb+z > k) continue;;
        res = max(res, w + nb + min(k-b-z, nz));
    }
    cout << res << "\n";
}