from sys import stdin
from math import hypot

def int_reader():
  for x in stdin.read().split(): yield int(x)
nextint = int_reader().next

T = nextint()

for t in range(T):
  N = nextint()
  A = []
  for n in range(N): A.append( (nextint(),nextint()) )
  result = 0
  for n in range(N/2):
    x1, y1 = A[n]
    x2, y2 = A[(n+1)%N]
    x3, y3 = A[(n+N/2)%N]
    x4, y4 = A[(n+N/2+1)%N]
    ux, uy = x2-x1, y2-y1
    nlen = hypot(ux,uy)
    nx, ny = uy/nlen, -ux/nlen
    wx, wy = x4-x1, y4-y1
    dist = abs(nx * wx + ny * wy)
    result += dist
  print "%.12f" % result