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

int main(){
	string s;cin >> s;
	vector<int> a(26);
	for(int i=0;i<s.size();++i){
		a.at(s.at(i)-'A')++;
	}
	bool ans=true;
	for(int i=0;i<26;++i){
		if(a.at(i)>1) ans=false;
	}
	if(ans) cout << "YES" << endl;
	else cout << "NO" << endl;
}