#include<stdio.h>

int main(void){
    int a,b,c,d;
    scanf("%d",&a);
    scanf("%d",&b);
    scanf("%d",&c);
    scanf("%d",&d);

    int turn=0;
    while(a<=0||c<=0){
        if(turn==0){
            c-=b;
            turn++;
        }
        else{
            a-=d;
            turn--;
        }
    }

    (a>c)?puts("Yes"):puts("No");

    return 0;
}