#include<iostream>
#include<vector>
#include<algorithm>
#include<functional>
#include<queue>
#include<stack>
#include<set>
#include<climits>
#include<cstdlib>
#include<cmath>
#include<string>

using namespace std;

#define INF 1 << 29
#define LL long long int

LL const MOD = 1000000007;

int main(){
    cin.tie(0);
    ios::sync_with_stdio(false);

    string str;
    cin >> str;
    vector<LL> c(30,0);

    for(int i = 0; i < str.size(); i++){
        c[str[i] - 'A']++;
        if(c[str[i] - 'A'] > 1){
            cout << "NO" << endl;
            return 0;
        }
    }    

    cout << "YES" << endl;
    
    return 0;
}