#include<iostream>
#include<string>
using namespace std;
int main(){
    string s;cin>>s;
    int a[26]={};
    for(char c:s)a[c-'A']++;
    for(int i=0;i<26;++i)if(a[i]>=2){cout<<"NO"<<endl;return 0;}
    cout<<"YES"<<endl;
}