secvente infopro C1

#include <bits/stdc++.h>
#define INF 0x3f3f3f3f

using namespace std;

ifstream fin("secvente.in");
ofstream fout("secvente.out");

int main() {
    fin.sync_with_stdio(false);
    fout.sync_with_stdio(false);
    fin.tie(nullptr);
    fout.tie(nullptr);
    int N, t;
    string s;
    fin >> N >> t >> s;
    s = '0' + s;
    int cnt1 = 0;
    for(char x : s)
        cnt1 += (x == '1');
    if(2 * t > cnt1 || 2 * t > N) {
        fout << -1;
        return 0;
    }
    vector < int > start(N + 2, INF);
    start[1] = 0;
    for(int i = 1; i <= t; ++i)
        if(s[i] == '0')
            ++start[1];
    for(int i = t + 1; i <= N; ++i) {
        start[i - t + 1] = start[i - t];
        if(s[i - t] == '0')
            --start[i - t + 1];
        if(s[i] == '0')
            ++start[i - t + 1];
    }
    vector < int > mn(N + 2, INF);
    for(int i = N; i > 0; --i)
        mn[i] = min(start[i], mn[i + 1]);
    int ans = INF;
    for(int i = 1; i <= N - 2 * t + 2; ++i)
        ans = min(ans, start[i] + mn[i + t]);
    if(ans == INF)
        ans = -1;
    fout << ans;
}