import sys
sys.setrecursionlimit(10**6)
inf=float('inf')

N=int(input())
dp=[0]*(N+1)
dp[0]=1
for i in range(N):
    if i+1<=N:
        dp[i+1]+=dp[i]
    if i+2<=N:
        dp[i+2]+=dp[i]
print(dp[N])