#include <bits/stdc++.h>
using namespace std;
 
int main() {
  int A, B, C, D;
  bool gudge = true;
  cin >> A >> B >> C >> D;
  
  while(gudge){
  A = A - D;
  B = B - C;
    
    if(A <= 0){
    gudge = false;
    cout << "No" << endl;
    }
    else if(B <= 0){
    gudge = false;
    cout << "Yes" << endl;
    }
  }
}