def a(k, memo={0 : 4, 1 : 3}):
    if k in memo: return memo[k]

    memo[k] = (19 * a(k - 1, memo) - 12 * a(k - 2, memo)) / 4
    return memo[k]

if __name__ == '__main__':
    k = int(input())
    print("{0:f}".format(a(k)))