#include<iostream> #include<cstdio> #include<cstring> #include<cmath> using namespace std; int main(){ string s1; cin>>s1; int len=s1.size(); for(int i=0;i<len;i++){ int sum=0; for(int j=0;j<=len;j++){ if(s1[i]==s1[j]){ sum++; } } if(sum==1){ cout<<s1[i]; return 0; } } cout<<"no"; return 0; }