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

int A, B, C, D;

int main(){
  cin >> A >> B >> C >> D;

  while(A > 0 && C > 0){
    C -= B;
    if(C <= 0){ cout << "Yes" << endl; break; }
    A -= D;
    if(A <= 0){ cout << "No" << endl; break; }
  }

  return 0;

}