#include <bits/stdc++.h>
using namespace std;

const string YES = "Yes";
const string NO = "No";

void solve(long long A, long long B, long long C, long long D)
{
    while (A > 0 && C > 0)
    {
        C = max(C - B, 0LL);
        if (C == 0LL)
        {
            cout << YES << endl;
            return;
        }
        A = max(A - D, 0LL);
        if (A == 0LL)
        {
            cout << NO << endl;
            return;
        }
    }
}

// Generated by 1.1.6 https://github.com/kyuridenamida/atcoder-tools  (tips: You use the default template now. You can remove this line by using your custom template)
int main()
{
    long long A;
    scanf("%lld", &A);
    long long B;
    scanf("%lld", &B);
    long long C;
    scanf("%lld", &C);
    long long D;
    scanf("%lld", &D);
    solve(A, B, C, D);
    return 0;
}
