题解 | #统计每个月兔子的总数#

month = int(input())
def tuzi(month):
    new_num1 = 1
    new_num2 = 0
    old_num = 0
    for i in range(month-1):
        old_num += new_num2
        new_num2 = 0
        new_num2 += new_num1
        new_num1 = 0 
        new_num1 += old_num
    total_num = new_num1 + new_num2 + old_num
    return total_num
print(tuzi(month))