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