import sys
stdin=sys.stdin

ip=lambda: int(sp())
fp=lambda: float(sp())
lp=lambda:list(map(int,stdin.readline().split()))
tp=lambda:tuple(map(int,stdin.readline().split()))
sp=lambda:stdin.readline().rstrip()
yp=lambda:print('Yes')
np=lambda:print('No')

n=ip()
dp=[0 for _ in range(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[-1])