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

int main(){
	cin.tie(0),ios::sync_with_stdio(false);
	string s; cin>>s;
	vector<int>v(26,0);
	for(auto&&i:s)++v.at(i-'A');
	cout<<(*max_element(v.begin(),v.end())>1?"NO"s:"YES"s)<<"\n"s;
}