#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <math.h>
#define ll long long

int main(void)
{
    int a, b, c, d;
    scanf("%d%d%d%d", &a, &b, &c, &d);
    while (a > 0 && c > 0)
    {
        c = c - b;
        a = a - d;
    }
    if (a <= 0 && c <= 0)
    {
        printf("Yes\n");
    }
    else if (a <= 0)
    {
        printf("No\n");
    }
    else
    {
        printf("Yes\n");
    }

    return 0;
}