#include <stdio.h>

int main()
{
    int a,b,c,d;

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

    while(1)
    {        c -= b;

        if(c <= 0)
            break;
        a-=d;

        if(a<=0)
            break;


    }

    if(a <= 0)
        printf("No\n");
    if(c <= 0)
        printf("Yes\n");

    return 0;
}
