# include<iostream> # include<cstring> using namespace std; int main(){ string a; int a_len,s=0; cin>>a; a_len=a.size(); int b[100000]={0}; for(int i=0;i<a_len;i++){ for(int j=0;j<a_len;j++){ if(a[i]==a[j]) b[i]++; } } for(int i=0;i<a_len;i++){ if(b[i]==1){ cout<<a[i]; return 0; } } cout<<"no"; return 0; }