#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(){ string s; int letters[26]={0},len,sum=0,i; getline(cin,s); len=s.length(); for(i=0;i<len;i++){ letters[s[i]-'a']++; } for(i=0;i<len;i++){ if(letters[s[i]-'a']==1){ cout<<s[i]<<endl; return 0; } } cout<<"no"<<endl; return 0; }