#include<stdio.h>
int main()
{
    long long int a,b,c=0,o,e,d=1,i,t,j,n,x,y,k,m,l,r=0;
    scanf("%lld%lld%lld%lld",&a,&b,&c,&d);
    i=c/b;
    j=a/d;
    if(i<j){printf("Yes\n");}
    else if(i==j)
    {
        if((c%b==0&&a%d>=0)||(c%b>0&&a%d>0)){printf("Yes\n");}
        else{printf("No\n");}
    }
    else
    {
        if(i-j==1&&c%b==0&&a%d!=0){printf("Yes\n");}
        else
        {
        printf("No\n");
        }
    }


}
