#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 -1;
}