#include <bits/stdc++.h>
#define PI 3.14159265359
using namespace std;

int main() {
	string S;
	cin >> S;

	bool b = true;
	vector<int> v(26);
	for (int i = 0; i < S.size(); i++) {
		int n = (int)S.at(i) - 'A';
		if (v.at(n)) {
			b = false;
			break;
		}
		else {
			v.at(n)++;
		}
	}

	cout << (b ? "YES" : "NO") << endl;
}