#include    <stdio.h>

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

    fscanf(stdin, "%d %d %d %d", &a, &b, &c, &d);

    while (1) {
	// T's turn
	c -= b;
	if (c <= 0) {
	    printf("Yes\n");
	    return 0;
	}

	// A's turn
	a -= d;
	if (a <= 0) {
	    printf("No\n");
	    return 0;
	}
    }

    return 0;
}
