saber

#include <iostream>
#include <map>

using namespace std;
map<char,int> S;

int main()
{
    string s;
    cin >> s;
    for(auto c:s) S[c] ++;

    for(auto c:s)
    {
        if(S[c] == 1)
        {
            cout<<c;
            return 0;
        }

    }
    cout<<"no";
}