func_code_string: #include <bits/stdc++.h>   using namespace std;   int main() {     ios_base::sync_with_stdio(0);     cin.tie(0);     cout.tie(0);     int n;     cin >> n;     string s;     cin >> s;     map<string, int> gram;     for (int i = 0; i < n - 1; i++) ++gram[s.substr(i, 2)];     int cnt = 0;     string ans =   ;     for (auto e : gram)       if (e.second > cnt) cnt = e.second, ans = e.first;     cout << ans;   }   