#include <bits/stdc++.h>   using namespace std;   string s;   long long k, n;   int index_1[(int)(1e6 + 5)], num = 0;   void solve() {     cin >> k >> s;     n = s.size();     if (k == 0) {       long long last = 0, ans = 0;       for (int i = 0; i < n; i++) {         if (s[i] ==  0 )           last++;         else {           ans += last * (last + 1) / 2;           last = 0;         }       }       ans += last * (last + 1) / 2;       cout << ans;       return;     }     for (int i = 0; i < n; i++) {       if (s[i] ==  1 ) index_1[num++] = i;     }     long long ans = 0;     for (int i = k - 1; i < num; i++) {       long long t1 = n - 1 - index_1[i] + 1;       if (i < num - 1) t1 = index_1[i + 1] - index_1[i];       long long t2 = index_1[i - (k - 1)] - 0 + 1;       if (i - (k - 1) > 0) t2 = index_1[i - (k - 1)] - index_1[i - (k - 1) - 1];       ans += t1 * t2;     }     cout << ans;   }   int main() {     ios_base::sync_with_stdio(false);     cin.tie(0);     int t = 1;     while (t--) {       solve();     }   }   