input_str = STDIN.gets
n = input_str.to_i

$result = []
$result[0] = 1
$result[1] = 1
# for num in 2..n do
#   result[num] = result[num - 1] + result[num - 2]
# end
for i in 0..n do
  $result[i] = 0
end

$result[0] = 1
$result[1] = 1

def fib num
  if $result[num] != 0
    return $result[num]
  end
  a = fib (num - 1)
  b = fib (num - 2)
  $result[num] = a + b

  return $result[num]
end

fib n
puts $result[n]

