#include<stdio.h>
#include<stdlib.h>
int main()
{
    int a,b,c,d;
    scanf("%d",&a);
    scanf("%d",&b);
    scanf("%d",&c);
    scanf("%d",&d);
    
    for(;;)
    {
        a-=d;
        c-=d;
        if(a<=0||c<=0)
        {
        if(a<=0)
        {
            printf("NO\n");
            break;
        }
        if(c<=0)
        {
            printf("YES\n");
            break;
        }
        }
    }
    return 0;
}
