#include <math.h>

#include <algorithm>
#include <cstring>
#include <iostream>
#include <string>
#include <vector>
using namespace std;
#define rep(i, n) for (int i = 0; i < n; i++)
using ll = long long;

int main() {
  int a, b, c, d;
  cin >> a >> b >> c >> d;

  while (1) {
    c -= b;
    if (c <= 0) {
      cout << "Yes";
      break;
    }
    a -= d;
    if (a <= 0) {
      cout << "No";
      break;
    }
  }
  return 0;
}
