#include <iostream>
#include <string>
#include <vector>
using namespace std;
int main(){
	string S;
	int N = S.size();
	vector<int> cnt(26, 0);
	for (int i = 0; i < N; i++){
		cnt[S[i] - 'A']++;
	}
	bool ok = true;
	for (int i = 0; i < 26; i++){
		if (cnt[i] > 1){
			ok = false;
		}
	}
	if (ok){
		cout << "YES" << endl;
	} else {
		cout << "NO" << endl;
	}
}