27行解决
#include <iostream>
#include <string>
#include <unordered_map>
using namespace std;
int main() {
string s;
cin >> s;
unordered_map<char, int> count;
for (char c : s) {
count[c]++;
}
for (char c : s) {
if (count[c] == 1) {
cout << c << endl;
return 0;
}
}
cout << "no" << endl;
return 0;
}