CF617B.Chocolate

Bob loves everything sweet. His favorite chocolate bar consists of pieces, each piece may contain a nut. Bob wants to break the bar of chocolate into multiple pieces so that each part would contain exactly one nut and any break line goes between two adjacent pieces.

You are asked to calculate the number of ways he can do it. Two ways to break chocolate are considered distinct if one of them contains a break between some two adjacent pieces and the other one doesn't.

Please note, that if Bob doesn't make any breaks, all the bar will form one piece and it still has to have exactly one nut.

鲍勃喜欢所有甜食。他最喜欢的巧克力棒由若干小块组成，每一块中可能含有一个坚果。鲍勃希望将这块巧克力棒分割成若干部分，使得每一部分恰好包含一个坚果，且每次断裂都必须发生在两个相邻小块之间。

你需要计算他完成这一分割的方案数。如果两种分割方式在某两个相邻小块之间存在断裂（即一种方式在此处断裂而另一种不在此处断裂），则认为它们是不同的方案。

请注意：如果鲍勃不进行任何断裂，则整块巧克力棒构成一个部分，此时它也必须恰好包含一个坚果。

The first line of the input contains integer n (1 ≤ n ≤ 100) — the number of pieces in the chocolate bar.

The second line contains n integers a__i (0 ≤ a__i ≤ 1), where 0 represents a piece without the nut and 1 stands for a piece with the nut.

输入的第一行包含一个整数 $n$（$1 \leq n \leq 100$）—— 表示巧克力条中的块数。

第二行包含 $n$ 个整数 $a_i$（$0 \leq a_i \leq 1$），其中 $0$ 表示不含坚果的块，$1$ 表示含坚果的块。

Print the number of ways to break the chocolate into multiple parts so that each part would contain exactly one nut.

输出将巧克力分割成多个部分的方法数，使得每一部分恰好包含一颗坚果。

In the first sample there is exactly one nut, so the number of ways equals 1 — Bob shouldn't make any breaks.

In the second sample you can break the bar in four ways:

10|10|1

1|010|1

10|1|01

1|01|01

在第一个样例中，恰好有一颗坚果，因此方案数为 1 —— Bob 不需要进行任何切割。

在第二个样例中，巧克力棒可以有四种切割方式：

10|10|1

1|010|1

10|1|01

1|01|01