#include<iostream>
#include<map>
#include<string>

using namespace std;

int main() {

	string str;
	cin >> str;
	map<char, int> mp;
	for (char c = 'A';c <= 'Z';c++) {
		mp[c] = 0;
	}

	for (int i = 0;i < str.size();i++) {
		char moji = str[i];
		mp[moji]++;
	}

	for (char c = 'A';c <= 'Z';c++) {
		if (mp[c] >= 2) {
			cout << "NO" << endl;
			return 0;
		}
	}

	cout << "YES" << endl;
	
	return 0;
}