#include <stdio.h>

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

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

    taka = a / d;
    if (a % d)
        taka++;
    ao = c / b;
    if(c % b)
        ao++;
    
    if (taka >= ao)
        printf("Yes\n");
    else 
        printf("No\n");
    
    return 0;
}