#include <iostream>
#include <string>
#include <algorithm>
#include <vector>
#define rep(i, a, b) for(int i = (a); i < (b); i++)
#define ill long long
using namespace std;

int main() {
  int a, b, c, d;
  cin >> a >> b >> c >> d;
  for(int i = 0; 1; i++) {
    if(i % 2 == 0) {
      c -= b;
      if(c <= 0) {
        cout << "Yes";
        return 0;
      }
    } else {
      a -= d;
      if(a <= 0) {
        cout << "No";
        return 0;
      }
    }
  }
}