github.com/captn3m0/codechef.git

---
category_name: easy
problem_code: REVERSE
problem_name: 'Chef and Reversing'
languages_supported:
    - ADA
    - ASM
    - BASH
    - BF
    - C
    - 'C99 strict'
    - CAML
    - CLOJ
    - CLPS
    - 'CPP 4.3.2'
    - 'CPP 4.9.2'
    - CPP14
    - CS2
    - D
    - ERL
    - FORT
    - FS
    - GO
    - HASK
    - ICK
    - ICON
    - JAVA
    - JS
    - 'LISP clisp'
    - 'LISP sbcl'
    - LUA
    - NEM
    - NICE
    - NODEJS
    - 'PAS fpc'
    - 'PAS gpc'
    - PERL
    - PERL6
    - PHP
    - PIKE
    - PRLG
    - PYTH
    - 'PYTH 3.4'
    - RUBY
    - SCALA
    - 'SCM guile'
    - 'SCM qobi'
    - ST
    - TCL
    - TEXT
    - WSPC
max_timelimit: '2'
source_sizelimit: '50000'
problem_author: berezin
problem_tester: null
date_added: 9-03-2014
tags:
    - aug14
    - berezin
    - easy
    - graph
    - shortest
editorial_url: 'http://discuss.codechef.com/problems/REVERSE'
time:
    view_start_date: 1407749400
    submit_start_date: 1407749400
    visible_start_date: 1407749400
    end_date: 1735669800
    current: 1493558181
layout: problem
---
All submissions for this problem are available.###  Read problems statements in [Mandarin Chinese](http://www.codechef.com/download/translated/AUG14/mandarin/REVERSE.pdf) and [Russian](http://www.codechef.com/download/translated/AUG14/russian/REVERSE.pdf).

Sometimes mysteries happen. Chef found a directed graph with **N** vertices and **M** edges in his kitchen!

The evening was boring and chef has nothing else to do, so to entertain himself, Chef thought about a question "What is the minimum number of edges he needs to reverse in order to have at least one path from vertex **1** to vertex **N**, where the vertices are numbered from **1** to **N**.

### Input

Each test file contains only one test case.

The first line of the input contains two space separated integers **N** and **M**, denoting the number of vertices and the number of edges in the graph respectively. The **i**th line of the next **M** lines contains two space separated integers **Xi** and **Yi**, denoting that the **i**th edge connects vertices from **Xi** to **Yi**.

### Output

In a single line, print the minimum number of edges we need to revert. If there is no way of having at least one path from **1** to **N**, print **-1**.

### Constraints

- **1 ≤ N, M ≤ 100000 = 105**
- **1 ≤ Xi, Yi ≤ N**
- There can be multiple edges connecting the same pair of vertices, There can be self loops too i.e.  **Xi = Yi**

### Example

<pre><b>Input:</b>
7 7
1 2 
3 2
3 4
7 4
6 2
5 6
7 5

<b>Output:</b>
2
</pre>### Explanation

We can consider two paths from **1** to **7**:

- **1-2-3-4-7**
- **1-2-6-5-7**

In the first one we need to revert edges **(3-2), (7-4)**. In the second one - **(6-2), (5-6), (7-5)**. So the answer is **min(2, 3) = 2**.