# coding: utf-8
import array, bisect, collections, heapq, itertools, math, random, re, string, sys, time
sys.setrecursionlimit(10 ** 7)
INF = 10 ** 20
MOD = 10 ** 9 + 7
 
 
def II(): return int(input())
def ILI(): return list(map(int, input().split()))
def IAI(LINE): return [ILI() for __ in range(LINE)]
def IDI(): return {key: value for key, value in ILI()}
 
 
def solve(N):
    dp = [0] * (N + 1)
    dp[0] = 1
    dp[1] = 1

    def move(now=N):
        if dp[now] != 0:
            return dp[now]

        else:
            dp[now] = move(now - 1) + move(now - 2)
            return dp[now]

    ans = move()

    return ans

def main():
    N = II()
    print(solve(N))
 
 
if __name__ == "__main__":
    main()