#include <iostream>
#include <string>

int main()
{
    std::string S;
    std::cin >> S;
    
    int n = (signed)S.size();
    bool flag = true;
    for(int i = 0;i < n - 1;i++)
    {
        for(int j = i + 1;j < n;j++)
        {
            if(S[i] == S[j])
            {
                flag = false;
            }
        }
    }
    if(flag)
    {
        std::cout << "YES" <<std::endl;
    }
    else
    {
        std::cout << "NO" <<std::endl;
    }
    
    return 0;
}