https://www.acmicpc.net/problem/1159
#include <iostream>
#include <string>
using namespace std;
int n{};
int arr[26];
string Result;
int main()
{
cin >> n;
for (int i = 0; i < n; i++)
{
cin >> Result;
arr[Result[0] - 'a']++;
}
Result = "";
for (int i = 0; i < 26; i++)
{
if (arr[i] >= 5)
Result += (char)(i + 'a');
}
if (Result == "")
cout << "PREDAJA" << endl;
else
cout << Result << endl;
}