#include <bits/stdc++.h> using namespace std; int main() { string s; int k; cin >> k >>s ; int b=s.size(); int c = 0; for (int i = 0; i < b; i++) { if (i == 0 || s[i] != s[i-1]) { c = 1; } else { c++; } if (c >= k) { cout << s[i] << endl; return 0; } } cout << "No" << endl; return 0; }