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


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