# expdist2 
# Fig. 22.3 
# input: 10000

import math, random

n = int(input("n=? "))
sum = 0
d = math.sqrt(3)
for i in range(n): 
  while True:
    x = random.random() 
    y = random.random() 
    if y < d*(0.5 - abs(x - 0.5)):
      break
  while True:
    z = random.random() 
    u = random.random() 
    if u < d*(0.5 - abs(z - 0.5)):
      break
  dist = math.sqrt((x-z)*(x-z) + (y-u)*(y-u))
  sum += dist
print(f"exp. dist. == {sum/n:.6f}")