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

int main()
{
	string s;
	cin >> s;
	int a[26]{};
	for (auto c : s)
	{
		a[c - 'A']++;
	}
	for (auto aa : a)
	{
		if (1 < aa)
		{
			cout << "NO" << endl;
			return 0;
		}
	}
	cout << "YES" << endl;
	return 0;
}