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

signed main(){
	string S;
	int temp[30] = {}, a = 1;
	cin>>S;
	
	for(int i = 0; i < S.size(); i++){
		temp[S[i] - 'A']++;
	}
	for(int i = 0; i < 26; i++){
		if(temp[i] >= 2)a=0;
	}
	
	cout<<(a?"YES":"NO")<<endl;
	
	return 0;
}