Problem:
Score : 500 points

Problem Statement

Rng has a connected undirected graph with N vertices.
Currently, there are M edges in the graph, and the i-th edge connects Vertices A_i and B_i.

Rng will add new edges to the graph by repeating the following operation:

Operation: Choose u and v (u \neq v) such that Vertex v can be reached by traversing exactly three edges from Vertex u, and add an edge connecting Vertices u and v. It is not allowed to add an edge if there is already an edge connecting Vertices u and v.

Find the maximum possible number of edges that can be added.

Constraints

2 \leq N \leq 10^5

1 \leq M \leq 10^5

1 \leq A_i,B_i \leq N

The graph has no self-loops or multiple edges.

The graph is connected.

Input

Input is given from Standard Input in the following format:

N M
A_1 B_1
A_2 B_2
:
A_M B_M

Output

Find the maximum possible number of edges that can be added.

Sample Input 1

6 5
1 2
2 3
3 4
4 5
5 6

Sample Output 1

4

If we add edges as shown below, four edges can be added, and no more.

Sample Input 2

5 5
1 2
2 3
3 1
5 4
5 1

Sample Output 2

5

Five edges can be added, for example, as follows:

Add an edge connecting Vertex 5 and Vertex 3.

Add an edge connecting Vertex 5 and Vertex 2.

Add an edge connecting Vertex 4 and Vertex 1.

Add an edge connecting Vertex 4 and Vertex 2.

Add an edge connecting Vertex 4 and Vertex 3.

Solution in Ruby (2.3.3) (judge verdict: Accepted)

N,M = gets.split.map(&:to_i)
$es = {}
M.times {
  a,b = gets.split.map(&:to_i)
  $es[a] ||= {}; $es[b] ||= {}
  $es[a][b] = $es[b][a] = 1
}

$parity = Array.new(N+1, nil)


ns = [1]
pa = 0
consistent = true
while ns.size > 0
  ns.each{ |n| $parity[n] = pa }
  pa ^= 1
  ks = {}
  ns.each{ |n|
    $es[n].keys.each{ |m|
      if $parity[m]
        if $parity[m] != pa
          consistent = false
          break
        end
        next
      end
      ks[m] = 1
    }
  }
  break if !consistent
  ns = ks.keys
end

if consistent
  a,b = $parity.count(1), $parity.count(0)
  p a*b - M
else
  p N*(N-1)/2-M
end