CODE

#include <iostream>

using namespace std;

int counts[26];
string s;

int main(void) {
  cin >> s;
  for (const auto& c : s) ++counts[c - 'a'];
  for (const auto& c : s) if (counts[c - 'a'] == 1) return putchar(c), 0;
  return puts("no"), 0;
}