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

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

	int N = S.size();
	vector<int> n( 26 );
	for( int i = 0; i < N; i++ ) {
		n[ S[i] - 'A' ]++;
	}
	string ans = "YES";
	for( int i = 0; i < 26; i++ ) {
		if( n[i] > 1 ) ans = "NO";
	}

	cout << ans << endl;
}