#include<iostream>
#include<string>
using namespace std;
int main()
{
	string str;
	bool flg = false;
	int val[25];
	for (int i = 0; i < 25; i++)val[i] = 0;

	cin >> str;

	for (int i = 0; i < str.length(); i++) {
		val[str[i] - 'A']++;
		if (val[str[i] - 'A'] > 1) {
			flg = true;
			break;
		}
	}
	if (flg == true)cout << "NO" << endl;
	else cout << "YES" << endl;
	return 0;
}