def fib n
  res = Array.new(n + 1, 0)
  res[0] = 1
  res[1] = 1
  (2..n).each do |i|
    res[i] = res[i - 1] + res[i - 2]
  end
  res
end

def main
  fibs = fib 44
  n = gets.chomp.to_i
  puts fibs[n]
end

main