#include <bits/stdc++.h>   using namespace std;   vector<int> me;   long long sum(long long x) { return (x * (x + 1)) / 2; }   int main() {     int k;     string s;     cin >> k >> s;     for (int i = 0; i < s.size(); i++) {       if (s[i] ==  1 ) {         me.push_back(i);       }     }     long long ans = 0, cnt = 0, idx = -1;     if (k == 0) {       for (int i = 0; i < s.size(); i++) {         if (s[i] ==  1 ) {           ans += sum(cnt);           cnt = 0;         } else {           cnt++;         }       }       ans += sum(cnt);     } else {       long long fst = -1;       for (int i = 0; i < me.size(); i++) {         int idx = me[i];         cnt = 0;         if ((i + k - 1) == me.size() - 1) {           ans += ((idx - fst) * (s.size() - me[i + k - 1]));         } else if (i + k - 1 < me.size() - 1) {           ans += ((idx - fst) * (me[i + k] - me[i + k - 1]));         }         fst = me[i];       }     }     cout << ans;     return 0;   }   