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

int main() {
  int a,b,c,d; cin >> a >> b >> c >> d;
  while(1){
    c = c - b;
    if(c <= 0) {
      cout << "Yes";
      break;
    }
    a = a - d;
    if(a <= 0) {
      cout << "No";
      break;
    }
  }
}
