#include <iostream>
#include <string>
using namespace std;

string s;
int cnt[26];

int main() {
	int i;
	
	cin >> s;
	for (i = 0; i < s.length(); i++) cnt[s[i] - 'A']++;
	for (i = 0; i < 26; i++) if (cnt[i] >= 2) break;
	
	if (i < 26) cout << "NO" << endl;
	else cout << "YES" << endl;
	return 0;
}