#include<stdio.h>
int main(void)
{
    int a,b,c,d;
    scanf("%d %d %d %d",&a,&b,&c,&d);
    while(1)
    {
        printf("c=%d\n",c);
        if(c<=0)
        {
            printf("Yes");
            break;
        }
                a -= d;
        if(a<=0)
        {
            printf("No");
            break;
        }
    }
    return 0;
}