k = int(input())
ans = [(0, 0)]

for i in range(1, k):
    x = ans[i-1][1] + 1
    ans.append((x, x + i))


i, j = ans[-1][0], ans[-1][1]
a = [(i*2) + 1 + (x*2) for x in range(k)]
print(sum(a))