heyman

#include<bits/stdc++.h>
using namespace std;
int zf[27] = {0};
int main(){
    string s; cin >> s;
    int l = s.size();
    for(int i = 0;i < l;i++) zf[s[i] - 'a']++;
    char ans;
    bool have_answer = 0;
    for(int i = 1;i <= 26;i++){
        if(zf[i] == 1){
            ans = i + 'a';
            have_answer = 1;
            break;
        }
    }
    if(have_answer) cout << ans;
    else cout << "no";
    return 0;
}