# include<iostream> # include<string> # include<cstring> using namespace std; int main(){ int n,b[26]={0}; string a; cin>>a; n=a.size(); for(int i=0;i<n;i++){ b[a[i]-'a']++; } for(int i=0;i<n;i++){ if(b[a[i]-'a']==1){ cout<<a[i]; return 0; } } cout<<"no"; return 0; }