#include <stdio.h>
int main()
{
    int a, b, c, d;
    scanf("%d %d %d %d", &a, &b, &c, &d);

    while (a > 0)
    {
        c = c - b;
        if (c < 0 || c == 0)
        {
            printf("Yes");
            return 0;
        }

        a = a - d;
    }