#include <iostream>
#include <string>
#include <vector>
using namespace std;
int main(int argc, char* argv[])
{
	string S;
	cin>>S;
	vector<int> A(26,0);
	int i;
	for (i=0;i<S.length();i++){
		int x=S[i]-'A';
		A[x]++;
		if (A[x]==2){
			cout<<"NO"<<endl;
			return 0;
		}
	}
	cout<<"YES"<<endl;
	return 0;
}