#include<bits/stdc++.h>
int main(){
    std::string s;std::cin>>s;
    std::sort(s.begin(),s.end());
    for(int i=0;i<(int)s.length()-1;i++){
        if(s.at(i)==s.at(i+1)){
            std::cout<<"NO"<<std::endl;
            return 0;
        }
    }
    std::cout<<"YES"<<std::endl;
}