# d + [d/2] = x
# [d/2] = x - d
# x-d <= d/2 < x-d+1
# 2/3 x <= d < 2/3 (x + 1)
# ceil(2/3 x) <= d < ceil(2/3 (x + 1))
d = int(input())
l, r = d, d + 1
ans = d
while l < r:
    ans = l
    l, r = (2 * l + 2) // 3, (2 * r + 2) // 3
print(ans)