#include <stdio.h>

int main(){
  int a, b, c, d;
  scanf("%d%d%d%d", &a, &b, &c, &d);
  int x = 0, y = 0;
  while(c > 0){
  	c -= b;
  	x++;
  }
  while(a > 0){
  	a -= d;
  	y++;
  }
  if(x <= y) puts("Yes");
  else puts("No");
  return 0;
}