# print("Введите число N")
# N = int(input())
# 
# def fac(x: int): # факториал числа
    # return _fac (x*2, x)
# 
# def  _fac(x: int, y: int):
    # if x > y:
        # return (y * _fac(x, y+1))
    # else:
        # return y
    # 
# x = 0
# if N <= 12:
    # for i in range(1, N+1):
        # step = i**i
        # factorial = fac(i)
        # x += step / factorial
    # print(x)

N = int(input())
s = 0
for i in range(1, N + 1):
    p = 1
    for j in range(i, 2 * i + 1):
        p *= j
    s += i**2 / p
    
print(s)