#include <stdio.h>

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

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

    takahashihp = d/ a;
    aokihp = b / c;

    if (takahashihp <= aokihp){
        printf("Yes\n");
    } else {
        printf("No\n");
    }

}