#include <stdio.h>

int main(void){

  int A, B, C, D;
  scanf("%d %d %d %d",&A, &B, &C, &D);

  do{
	C = C - B;
	A = A - D;
  }while(A <= 0 | C <= 0);
  
  if(C<=0)
	  printf("Yes");
  else
	  printf("No");
           
  return 0;
}
