#include<stdio.h>
int main()
{
    int a,b,c,d,i;
    while(scanf("%d %d %d %d",&a,&b,&c,&d)!=EOF)
    {
        for(i=1;i>0;i++)
        {
            if(i%2!=0)
            {
                c=c-b;
                if(c<=0)
                {
                    printf("Yes\n");
                    i=-1;
                }
            }
            else
            {
                a=a-d;
                if(a<=0)
                {
                    printf("No\n");
                    i=-1;
                }
            }
        }
    }
    return 0;
}
