#include <bits/stdc++.h>   using namespace std;   long unsigned int combi(long unsigned int a) {     if (a == 0 || a == 1) return 0;     return ((a * (a - 1)) / 2);   }   int main() {     int n = 0;     cin >> n;     char arr[n];     int letras[26];     char temp = 0;     long unsigned int res = 0;     for (int i = 0; i < 26; i++) {       letras[i] = 0;     }     for (int i = 0; i < n; i++) {       cin >> temp;       cin.ignore(256,   n );       letras[temp - 97]++;     }     for (int i = 0; i < 26; i++) {       res += (combi(letras[i] - (letras[i] / 2)) + (combi(letras[i] / 2)));     }     printf( %lu , res);     return 0;   }   