#include <bits/stdc++.h>
#define rep(i, n) for (int i = 0; i < (n); i++)
using namespace std;
typedef long long ll;

int main()
{
    int a, b, c, d;
    cin >> a >> b >> c >> d;
    while(a > 0 && c > 0) {
        c -= b;
        if (c <= 0) {
            cout << "Yes" << endl;
            break;
        }
        a -= d;
        if (a <= 0) {
            cout << "No" << endl;
            break;
        }
    }
    
    return 0;
}