def solve(memo, p, n):
  if p in memo:
    return memo[p]
  
  res = 0
  if p == n:
    res = 1
    memo[p] = 1
  elif p > n:
    res = 0
  else:
    re1 = solve(memo, p + 1, n)
    memo[p + 1] = re1
    re2 = solve(memo, p + 2, n)
    memo[p + 2] = re2
    res = re1 + re2
  return res

n = int(input())

res = solve({}, 0, n)
print(res)