#include<iostream>
#include<string>
#include<vector>
#include<algorithm>
#include<cmath>
#include<stdio.h>
#include<queue>
#include <climits>
#include <map>
#include <set>
const int mod = 1e9 + 7;
const long long INF = 1LL << 60;
using namespace std;
typedef long long ll;

int main()
{
    string s;
    cin >> s;
    int a[26] = {0};
    for(int i = 0; i < s.size(); i++){
        a[s[i]-'A']++;
    }
    for(int i = 0; i < 26; i++){
        if(a[i] > 1){
            cout << "NO" << endl;
            return 0;
        }
    }
    cout << "YES" << endl;
}