#include <stdio.h>

#include <stdlib.h>
#include <string.h>
#include <math.h>
#include <stdlib.h>

#define N 200010
#define MAX 1000000000000000000
#define MOD 1000000007

#include <stdio.h>

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

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

    takahashi = (c + (b - 1)) / b;
    aoki = (a + (d - 1)) / d;

    if (takahashi <= aoki) {
        puts("Yes");
    } else {
        puts("No");
    }

    return 0;
}

