#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef pair<int, int> P;
#define rep(begin, i, end) for (int i = begin; i < (int)(end); i++)
#define all(v) v.begin(), v.end()
const int MOD = 1000000007;

int main()
{
    int A, B, C, D;
    cin >> A >> B >> C >> D;
    while (1)
    {

        C -= B;
        if (C <= 0)
        {
            cout << "Yes" << endl;
            return 0;
        }
        A -= D;
        if (A <= 0)
        {
            cout << "No" << endl;
            return 0;
        }
    }
}