#include <stdio.h>

void main() {
    int a, b, c, d;
    int t_hp, a_hp;

    scanf("%d %d %d %d", &a, &b, &c, &d);

    a_hp = c;
    t_hp = a;

    while(1){
        //Takahashi attack
        a_hp -= b;
        if(a_hp <= 0){
            printf("Yes\n");break;
        }
        //Aoki attack
        t_hp -= d;
        if(t_hp <= 0){
            printf("No\n");break;
        }
    }
}