#include <iostream>
#include <algorithm>
#include <vector>
using namespace std;
int main(void) {
	string s;
	cin >> s;
	vector<char> v(26, 0);
	for (int i = 0; i < s.size(); ++i) {
		++v[s[i] - 'A'];
	}
	int a = *max_element(v.begin(), v.end());
	cout << (a <= 1 ? "YES" : "NO") << endl;
	return 0;
}