#include <iostream>
#include <string>
using namespace std;
int main(void){
    
    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" << endl;
            }
        }
    }
    
    cout << "YES" << endl;
    
    
}