# expdist1 
# Fig. 22.2 
# input: 10000

import math, random

n = int(input("n=? "))
sum = 0
for i in range(n): 
  dx = random.random() - random.random() 
  dy = random.random() - random.random() 
  sum += math.sqrt(dx*dx + dy*dy)
print(f"expected dist == {sum/n:.6f}")