#include<bits/stdc++.h>
#define rep(i,a,b) for(int i=int(a);i<int(b);++i)
using namespace std;
typedef long long ll;
int INF = (1LL << 30) - 1;
int MOD = 1e9+7;
main(){
    string S;
    cin >> S;
    int cnt[26] = {};
    for(auto c:S){
        if(cnt[c - 'A']){
            cout << "NO" << endl;
            return 0;
        }
        cnt[c - 'A']++;
    }
    cout << "YES" << endl;
}