#include <bits/stdc++.h>
#define REP(i, a, n) for(ll i=a; i<n; i++)
#define RREP(i, a, n) for(ll i=n-1; i>=a; i--)
typedef long long ll;
const ll mod =1e9+7;
const ll inf =1e18;
using namespace std;

string S;
ll alp[26];
int main() {
    cin>>S;
    REP(i, 0, S.size()){
        alp[S[i]-'A']++;
    }

    bool ok=true;
    REP(i, 0, 26){
        if(alp[i]>1){
            ok=false;
            break;
        }
    }
    if(ok) cout<<"YES"<<endl;
    else cout<<"NO"<<endl;
    return 0;
}