一本通1130

#include <bits/stdc++.h>
#define rep(i,j,n) for(register int i=j;i<=n;i++)
#define Rep(i,j,n) for(register int i=j;i>=n;i--)
#define low(x) x&(-x)
using namespace std ;
typedef long long LL ;
const int inf = INT_MAX >> 1 ;
inline LL In() { LL res(0) , f(1) ; register char c ;
#define gc c = getchar()
    while(isspace(gc)) ; c == '-' ? f = - 1 , gc : 0 ;
    while(res = (res << 1) + (res << 3) + (c & 15) , isdigit(gc)) ;
    return res * f ;
#undef gc
}

string s ;
map < char , int > mp ;
inline void Ot() {
	mp.clear() ;
	getline(cin,s) ;
	rep(i,1,s.length()) mp[s[i-1]] ++ ;
	rep(i,1,s.length()) {
		if(mp[s[i-1]] == 1) {
			putchar(s[i-1]) ;
			return ;
		}
	}
	puts("no") ;
}
signed main() {
//  freopen("test.in","r",stdin) ;
    return Ot() , 0 ;
}