#include <bits/stdc++.h>
typedef unsigned long long ll;
#define INF 1000000000
using namespace std;
#define N 100000
int main(void){
    string s;
    cin>>s;
    sort(s.begin(),s.end());
    for(int i=0;i<s.size()-1;i++){
        if(s[i]==s[i+1]){
            cout<<"NO"<<endl;
            return 0;
        }
    }
    cout<<"YES"<<endl;
}