#include <bits/stdc++.h>
using namespace std;

int main() {

    string S;
    cin >> S;
    map<char, int> mp;
    int N = S.size();
    for(int i=0; i<N; i++) {
        mp[S[i]]++;
    }
    for(auto [n,m] : mp) {
        if(m > 1) {
            cout << "NO" << endl; 
            return 0;
        }
    }
    cout << "YES" << endl;
    return 0;

}