digits = int(input())
array = [2] * digits * 4
pi = ''

predigits = []

for digit in range(digits):
 array = [*map(lambda num: num * 10, array)]
 for index in range(len(array) - 1):
  numerator = len(array) - index - 1
  denominator = numerator * 2 + 1
  array[index + 1] += (array[index] // denominator) * numerator
  array[index] = array[index] % denominator

 quotient = array[-1] // 10

 if quotient == 9:
  predigits.append(9)

 elif quotient == 10:
  for num in predigits:
   pi += str((num + 1) % 10)
  predigits = [0]

 else:
  for num in predigits:
   pi += str(num)
  predigits = []
  predigits.append(quotient)

 array[-1] %= 10

print('3.' + pi[1:])