#include <bits/stdc++.h>
using namespace std;
#define int long long
const int MOD=1000000007;
const int INF=1e18;

signed main(){
    cin.tie(0);
	ios::sync_with_stdio(false);
    std::string s;
    std::cin >> s;
    int cnt[26] = {};
    for(int i = 0 ; i < s.size() ; i++){
        cnt[s[i]-'0']++;
        if (cnt[s[i]-'0']==2)
        {
            std::cout << "NO" << "\n";
            return 0;
        }
    }
    std::cout << "YES" << "\n";

    return 0;
}