Note

#include <iostream>

using namespace std;

int cnt[26];
string s;

int main()
{
    cin >> s;
    for (int i = 0; i < s.size(); i ++) cnt[s[i] - 'a'] ++; 
    // use array to store the information

    for (int i = 0; i < s.size(); i ++)
    {
        if (cnt[s[i] - 'a'] == 1)
        {
            cout << s[i] << endl;
            return 0;
        }
    }
    cout << "no" << endl;
    return 0;
}