#include <stdio.h>

#define lint long long int
#define N_MAX 2000



int main()
{
    int a, b, c, d;
    scanf("%d %d %d %d", &a, &b, &c, &d);
    
    int n_taka = c / b;
    if (c % b) n_taka++;
    
    int n_ao = a / d;
    if (a % d) n_ao++;
    
    if (n_taka <= n_ao) printf("Yes\n");
    else printf("No\n");
}
