#!/usr/bin/env python3
#coding:utf-8

import math
import string
from sys import stdin
# import numpy as np
# from matplotlib import pyplot as plt

	
def main():
	read=stdin.readline

	#edit here!
	n=int(read())
	dp=[0]*(n+5)
	dp[0]=1
	for i in range(n):
		dp[i+1]+=dp[i]
		dp[i+2]+=dp[i]
	print(dp[n])
if __name__ == '__main__':
	main()