x = int(input())
p = 0
i = 0
li = ["a","a","b","b","a","b","b"]
ans = 0
s = 0
while s < 101:
  if i > len(li) - 1:
    s += 1  
    i = 0
  if li[i] == "a":
    p += 2
    ans += 2
  else:
    p -= 1
    ans += 1
  if p == x:
    print(ans)
    break
  i += 1