ll@n,@a[n],@b[n],c[n]{},d[n]{},m=n-1;
c[m]=a[n-1];
d[m]=b[n-1];
rrep(i,n-1){
	if(a[i]*d[m]<b[i]*c[m]){
		--m;
	}
	c[m]+=a[i];
	d[m]+=b[i];
}
double z=0;
rep(i,m,n){
	z+=c[i]<d[i]?c[i]+d[i]:2*sqrt(c[i]*d[i]);
}
wt(z);