#include<stdio.h>
int main() {
    int a, b, c, d;
    scanf("%d %d %d %d", &a, &b, &c, &d);
    while (a > 0 && c > 0)
    {
        c = c - b;
        if (c > 0)
        {
            a = a - d;
        }

    }
    if (c <= 0)
    {
        printf("Yes\n");
    }
    else
    {
        printf("No\n");
    }


    return 0;
}