There is a kind of rabbit , From the day after birth 3 A rabbit has been born every month since last month , The little rabbit grows to the third month and gives birth to another rabbit every month .
Example ： Suppose a rabbit 3 Months was born , So it's the first 5 A rabbit will be born every month from the beginning of next month .
There was a rabbit in January , If the rabbits don't die , Ask No n What's the total number of rabbits in a month ？
Data range ：
Input satisfaction 1≤n≤31
Input description ：
Enter a int An integer of type denotes the th n Months
Output description ：
Output the corresponding total number of Rabbits
Input ：
3
Output ：
2
