import sys

def sumOfGroup(k):
    k = k - 1
    sum_ = (k * (k + 1)) // 2
    odd1 = 2*(sum_ + 1) - 1
    odd2 = 2 * (sum_ + k + 1) - 1
    result = sum(range(odd1, odd2 + 1, 2))
    return result

if __name__ == "__main__":
    k = int(input().strip())
    answer = sumOfGroup(k)
    print(answer)