#include <bits/stdc++.h> using namespace std; int main() { string s; map<char, int> m; queue<char> q; cin >> s; for (char i : s) { m[i]++; q.push(i); } while (!q.empty()) { if (m[q.front()] == 1) { cout << q.front() << endl; exit(0); } q.pop(); } cout << "no" << endl; return 0; }