#include <bits/stdc++.h>
typedef long long i64;
using std::cout;
using std::endl;
using std::cin;

int main(){
	std::string s; cin >> s;
	sort(begin(s), end(s));
	
	for(int i = 0; i < s.size() - 1; i++) {
		if(s[i] == s[i + 1]) {
			cout << "NO" << endl;
			return 0;
		}
	}
	
	cout << "YES" << endl;
	return 0;
}