def main():
    n = int(input())
    
    dp = [0 for i in range(n + 1)]
    dp[0] = 1
    dp[1] = 1
    for i in range(2,n+1):
        dp[i] += dp[i - 1] + dp[i - 2]
    print(dp[n])


if __name__ == '__main__':
    main()