def nCr(n, r): result = 1 for i in range(1, r + 1): result = result * (n - i + 1) // i return result def sugoroku(N): limit = N // 2 + N % 2 num = N cnt = 0 while num >= limit: cnt += nCr(num, N - num) num = num - 1 return cnt if __name__ == '__main__': N = int(input()) print(sugoroku(N))