#include<stdio.h>
int main(void)
{
  int A,B,C,D,count;
  scanf("%d %d %d %d", &A, &B, &C, &D);
  while(A > 0 && C > 0){
    if(count % 2 == 0){
      C-=B;
    }else{
      A-=D
	}
    count++;
  }

  if(A <= 0){
    printf("No\n");
  }

  if(C <= 0){
    printf("Yes\n");
  }

  return 0;

}