#include <bits/stdc++.h>

using namespace std;

using ll = long long;

int main()
{
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    string s;
    cin >> s;

    sort(s.begin(),s.end());
    
    for (size_t i=0;i<s.size()-1;++i)
    {
        if (s[i]==s[i+1])
        {
            cout << "NO\n";
            return 0;
        }
    }

    cout << "YES\n";
    
    return 0;
}