tj

#include<bits/stdc++.h>
using namespace std;

int main()
{
    string a;
    cin>>a;
    vector<int> b = {0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0};
    for(int i = 0;i<a.size();i++)
        {
            b[a[i]-'a']++;
        }
    for(int i = 0;i<26;i++)
        {
            if(b[i]==1)
            {
                cout<<char('a'+i);
                return 0;
            }
        }
    cout<<"no";
}