#include <bits/stdc++.h>
using namespace std;
int s,n,h=0;
double ans=0;
struct NODE{
	int x, y;
	bool operator<(const NODE rhs)const{
		return x<rhs.x; }
} node[100];
int main() {
	cin>>s;
	while(s--){
		cin>>n;
		h=0,ans=0;
		cin>>node[0].x>>node[0].y;
		for(int i=1;i<n;i++){		
			cin>>node[i].x>>node[i].y;
		}
		sort(node,node+n);
		for(int i=n-2;i>=0;i--){
 
			if(node[i+1].y<node[i].y and node[i].y>h){
				//cout<<node[i].x<<endl;
				ans+=sqrt(  (node[i].x-node[i+1].x)*(node[i].x-node[i+1].x) + (node[i].y-node[i+1].y)*(node[i].y-node[i+1].y)  )/(node[i].y-node[i+1].y)*(node[i].y-h);
				h=node[i].y;
			}
		}
		cout<<fixed<<setprecision(2)<<ans<<endl;
 
	}
 
	return 0;
}

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MgoxMQoxMTAwIDEyMDAKMCA1MDAKMTQwMCAxMDAKNjAwIDYwMAoyODAwIDAKNDAwIDExMDAKMTcwMCA2MDAKMTUwMCA4MDAKMjEwMCAzMDAKMTgwMCA3MDAKMjQwMCA1MDAKMgowIDEwMDAKMTAwMCAw

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