#include<iostream> // cin\cout\endl #include<cstdio> //scanf()\printf() #include<cstring> // strcpy()\strcat()\strcmp()\strlen()\memset() #include<cmath> //sqrt()\pow()\abs()\ceil()\floor()\max()\min() using namespace std; int main(){ int a[26]={0}; string x; getline(cin,x); for(int i=0;i<x.length();i++){ a[x[i]-'a']++; } for(int i=0;i<x.length();i++){ if(a[x[i]-'a']==1){ cout<<x[i]<<endl; return 0; } } cout<<"no"<<endl; return 0; }