#include <iostream>
#include <algorithm>
using namespace std;
int main(){
    string s;cin>>s;
    int z = s.size();
    sort(s.begin(),s.end());s.erase(unique(s.begin(),s.end()),s.end());
    if(z == s.size())cout << "YES" << endl;
    else cout << "NO" << endl;
}