#include<string>
#include<iostream>
using namespace std;

int main() {
    string s;
    cin >> s;

    for (int i = 0; i < s.size(); i++){
        for (int j = i+1; j < s.size(); j++){
            if (s[i] == s[j]){
                cout << "NO\n";
                return 0;
            }
                
        }
    }
    cout <<  "YES\n";

}