#include <stdio.h>

struct st_pokemon //モンスターのステータス用構造体(体力・攻撃力)
{
	int hp;
	int attack;
};

void main(void)
{
	struct st_pokemon takahashi;
	struct st_pokemon aoki;
	int hp_judge	        = 0;
	int attack_judge 		= 0;
    int result				= 0;

	scanf( "%d %d %d %d", &takahashi.hp , &takahashi.attack , &aoki.hp , &aoki.attack );
	
	hp_judge            = takahashi.hp - aoki.hp;
  	attack_judge		= takahashi.attack - aoki.attack;
  
    result				= (attack_judge + 1) / ( hp_judge + 1 );

	if( result >= 0 )
	{
		printf("Yes");
	}
	else
	{
		printf("No");
	}
 
 	return;
}