N=int(input())
dp=[[0]*(N+1) for _ in range(N+1)]
dp[0][0]=1

for i in range(N):
    for j in range(N):
        if dp[i][j]:
            if j+1<=N:
                dp[i+1][j+1]+=dp[i][j]
            if j+2<=N:
                dp[i+1][j+2]+=dp[i][j]
ans=0
for i in range(N+1):
    ans+=dp[i][N]
print(ans)