using System;
using System.Collections;
using System.Collections.Generic;
using System.Linq;
using System.IO;
using System.Text;
using System.Globalization;
using System.Diagnostics;



class Myon
{
    public Myon() { }
    public static int Main()
    {
        new Myon().calc();
        return 0;
    }
    

    Scanner cin;

    List<int>[] es;

    void calc()
    {
        cin = new Scanner();
        int N = cin.nextInt();
        int M = cin.nextInt();

        es = new List<int>[N];
        for (int i = 0; i < N; i++)
        {
            es[i] = new List<int>();
        }

        int[] A = new int[M];
        int[] B = new int[M];
        for (int i = 0; i < M; i++)
        {
            A[i] = cin.nextInt() - 1;
            B[i] = cin.nextInt() - 1;
            es[A[i]].Add(B[i]);
            es[B[i]].Add(A[i]);
        }
        int[] color = new int[N];
        for (int i = 0; i < N; i++)
        {
            color[i] = -1;
        }
        color[0] = 0;
        Queue<int> q = new Queue<int>();
        q.Enqueue(0);
        bool isDouble = true;
        while(q.Count != 0)
        {
            int now = q.Dequeue();
            foreach (var next in es[now])
            {
                if(color[next] == -1)
                {
                    color[next] = 1 - color[now];
                    q.Enqueue(next);
                }
                else
                {
                    if(color[next] == color[now])
                    {
                        isDouble = false;
                    }
                }
            }
        }
        if (isDouble)
        {
            long AA = 0;
            for (int i = 0; i < N; i++)
            {
                if (color[i] == 0) AA++;
            }
            long BB = N - AA;
            Console.WriteLine((AA * BB) - M);
        }
        else
        {
            Console.WriteLine((N * (long)(N - 1) / 2) - M);
        }
    }
    
}



class Scanner
{
    string[] s;
    int i;

    char[] cs = new char[] { ' ' };

    public Scanner()
    {
        s = new string[0];
        i = 0;
    }

    public string next()
    {
        if (i < s.Length) return s[i++];
        string st = Console.ReadLine();
        while (st == "") st = Console.ReadLine();
        s = st.Split(cs, StringSplitOptions.RemoveEmptyEntries);
        if (s.Length == 0) return next();
        i = 0;
        return s[i++];
    }

    public int nextInt()
    {
        return int.Parse(next());
    }
    public int[] ArrayInt(int N, int add = 0)
    {
        int[] Array = new int[N];
        for (int i = 0; i < N; i++)
        {
            Array[i] = nextInt() + add;
        }
        return Array;
    }

    public long nextLong()
    {
        return long.Parse(next());
    }

    public long[] ArrayLong(int N, long add = 0)
    {
        long[] Array = new long[N];
        for (int i = 0; i < N; i++)
        {
            Array[i] = nextLong() + add;
        }
        return Array;
    }

    public double nextDouble()
    {
        return double.Parse(next());
    }


    public double[] ArrayDouble(int N, double add = 0)
    {
        double[] Array = new double[N];
        for (int i = 0; i < N; i++)
        {
            Array[i] = nextDouble() + add;
        }
        return Array;
    }
}

Measured memory_bytes: 29840