CF1139A.Even Substrings

普及/提高-

通过率：0%

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题目描述

You are given a string $s=s_1s_2\dots s_n$ of length $n$ , which only contains digits $1$ , $2$ , ..., $9$ .

A substring $s[l \dots r]$ of $s$ is a string $s_l s_{l + 1} s_{l + 2} \ldots s_r$ . A substring $s[l \dots r]$ of $s$ is called even if the number represented by it is even.

Find the number of even substrings of $s$ . Note, that even if some substrings are equal as strings, but have different $l$ and $r$ , they are counted as different substrings.

输入格式

The first line contains an integer $n$ ( $1 \le n \le 65000$ ) — the length of the string $s$ .

The second line contains a string $s$ of length $n$ . The string $s$ consists only of digits $1$ , $2$ , ..., $9$ .

输出格式

Print the number of even substrings of $s$ .

输入输出样例

输入#1
```
4
1234
```
输出#1
```
6
```
输入#2
```
4
2244
```
输出#2
```
10
```

说明/提示

In the first example, the $[l, r]$ pairs corresponding to even substrings are:

$s[1 \dots 2]$
$s[2 \dots 2]$
$s[1 \dots 4]$
$s[2 \dots 4]$
$s[3 \dots 4]$
$s[4 \dots 4]$

In the second example, all $10$ substrings of $s$ are even substrings. Note, that while substrings $s[1 \dots 1]$ and $s[2 \dots 2]$ both define the substring "2", they are still counted as different substrings.

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