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

int main() {
  
  int A;
  int B;
  int C;
  int D;
  cin >>A;
  cin >>B;
  cin >>C;
  cin >>D;
  int a;
   a=A-D;
  int b;
  b=C-B;
  int X;
 if(A%a==0){
   X=A/a;
 }
  else{
   X=(A+3)/a;
  }
  int Y;
  if(B%b==0){
   Y=B/b;
  }
  else{
   Y=(B+3)/b;
  }
  if(X<=Y){
    cout << "No" << endl;
  }
  else{
    cout << "Yes" <<endl;
  }
}
