n = int(input())
if n <= 2:
	print(n)
else:
	f = [0 for _ in range(n+1)]
	f[0] = 1
	f[1] = 1
	f[2] = 2
	for i in range(3, n+1):
		f[i] = f[i-1] + f[i-2]
	print(f[n])