#include<iostream>
using namespace std;

int main(){
  int A, B, C, D;
  cin >> A >> B >> C >> D;
  int a;
  while(true) {
    C -= B;
    if (C <= 0) {
      a = 0;
      break;
    }
    A -= D;
    if (A <= 0) {
      a = 1;
      break;
    }
  }
  if (a) cout << "No" << endl;
  else cout << "Yes" << endl;
}
  