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

int main(){
    string s;
    cin>>s;
    
    int cnt[26]={};
    for(char c:s){
        cnt[c-'A']++;
    }
    for(int i=0;i<26;++i){
        if(cnt[i]>1){
            cout<<"NO"<<endl;
            return 0;
        }
    }
    cout<<"YES"<<endl;
    return 0;
}