#include<bits/stdc++.h>

#define INF 1000000007
#define LINF 1000000000000000007

using namespace std;

typedef long long ll;
typedef pair<ll, ll> P;


string s;

int main(){
	cin >> s;
	bool b[26] = {0}, ans = 0;
	for(int i = 0; i < s.size(); i++){
		if(b[s[i]-'A']) ans = 1;
		b[s[i]-'A']=1;
	}
	if(!ans) cout << "YES" << endl;
	else cout << "NO" << endl;
	
	return 0;
}