from decimal import Decimal, getcontext

precision = int(input('Enter the precision: ')) + 1
if not (precision - 1):
    pi = 3
else:
    getcontext().prec = precision
    pi = sum([(1/Decimal(16)**k * (Decimal(4)/(8*k+1) - Decimal(2)/(8*k+4) - Decimal(1)/(8*k+5) - Decimal(1)/(8*k+6))) for k in range(precision)])
print(pi)