文件目录

#include <iostream>
using namespace std;
int main()
{
    string s;
    cin >> s;
    int a[128] = {};
    for (int i = 0; s[i]; i++)
        if (a[s[i]] > 1)
            continue;
        else
            a[s[i]]++;
    for (int i = 0; s[i]; i++)
        if (a[s[i]] == 1)
        {
            cout << s[i];
            return 0;
        }
    cout << "no";
    return 0;
}