tj

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

int main()
{
    string a;
    cin>>a;
    int b[26] = {0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0};
    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";
}