
```cpp
#include <iostream>
using namespace std;
const int N = 1000001;
int n, a[N];
string s;
int main(){
    bool flag = false;
    cin >> s;
    for(auto i : s){
        a[i - 'a']++;
    }
    for(int i = 0; i <= 26; i++){
        if(a[i] == 1){
            cout << char(i + 'a');
            flag = true;
            return 0;
        }
    }
    if(flag == false){
        cout << "no";
    }
    return 0;
}
```
