import bisect import copy import decimal import fractions import heapq import itertools import math import random import sys from collections import Counter, deque,defaultdict from functools import lru_cache,reduce from heapq import heappush,heappop,heapify,heappushpop,_heappop_max,_heapify_max def _heappush_max(heap,item): heap.append(item) heapq._siftdown_max(heap, 0, len(heap)-1) def _heappushpop_max(heap, item): if heap and item < heap[0]: item, heap[0] = heap[0], item heapq._siftup_max(heap, 0) return item from math import gcd as GCD read=sys.stdin.read readline=sys.stdin.readline readlines=sys.stdin.readlines N=int(readline()) dp=[0]*(N+1) dp[1]=1 dp[2]=2 for i in range(3,N+1): dp[i]=dp[i-1]+dp[i-2] ans=dp[N] print(ans)