#include<iostream>
#include<map>
#include<vector>
#include <algorithm>
#include<math.h>
using namespace std;


int main()
{
    string s;
    cin >> s;
    vector<int> a(26);
    for (int i = 0; i < s.size(); i++){
        if(!a[s[i] - 'A']) a[s[i] - 'A']++;
        else if (a[s[i] - 'A']){
            cout << "NO" << endl;
            return 0;
        }
    }
    cout << "YES" << endl;
}