#include <bits/stdc++.h>
using namespace std;
 
int main() {
	ios::sync_with_stdio(false);
	cin.tie(0); 
	
	vector<int> a(26, 0);
	string s;
	cin >> s;
	for(int i = 0; i < s.size(); i++) {
		if(a[s[i] - 'a'] == 0) a[s[i] - 'a']++;
		else {
			cout << "NO" << endl;
			return 0;
		}
	}
	cout << "YES" << endl;
	return 0;
}