5和7爆了

#include <iostream>
#include <string>
using namespace std;

int cnt;

int main(){
    string str;cin>>str;
    char c = 0;
    for(c = 'a';c <= 'z';c++){
        cnt = 0;
        for(int i = 0;i < str.size();i++){
            if(str[i] == c)cnt++;
        }
        if(cnt == 1)break;
    }
    if(c == 'z' + 1)cout<<"no";
    else cout<<c;
}