# include<iostream> # include<cstring> using namespace std; int main(){ string a,b; int a_len,b_len,s=0; cin>>a; a_len=a.size(); for(int i=0;i<a_len;i++){ s=1; for(int j=0;j<a_len;j++){ if(a[i]==a[j]){ s++; } } if(s==2){ cout<<a[i]; return 0; } } cout<<"no"; return 0; }