#include <bits/stdc++.h>
#define FOR(v, a, b) for(int v = (a); v < (b); ++v)
#define FORE(v, a, b) for(int v = (a); v <= (b); ++v)
#define REP(v, n) FOR(v, 0, n)
#define REPE(v, n) FORE(v, 0, n)
#define REV(v, a, b) for(int v = (a); v >= (b); --v)
#define ALL(x) (x).begin(), (x).end()
#define ITR(it, c) for(auto it = (c).begin(); it != (c).end(); ++it)
#define RITR(it, c) for(auto it = (c).rbegin(); it != (c).rend(); ++it)
#define EXIST(c,x) ((c).find(x) != (c).end())
#define LLI long long int
#define fst first
#define snd second
#ifndef M_PI
#define M_PI 3.14159265358979323846
#endif
#ifndef M_E
#define M_E 2.71828182845904523536
#endif
#ifdef DEBUG
#include <boost/core/demangle.hpp>
#define dump(x) cerr << "L" << __LINE__ << ": in " << __PRETTY_FUNCTION__ << " \e[32;1m" << boost::core::demangle(typeid(x).name()) << "\e[37m" << " " << (#x) << " = " << (x) << "\e[m" << endl;
#else
#define dump(x)
#endif
#define pln(x) cout << (x) << endl
#define gcd __gcd

using namespace std;
template <class T> constexpr T lcm(T m, T n){return m*n/gcd(m,n);}

template <typename T> using V = vector<T>;
template <typename T, typename U> using P = pair<T,U>;
template <typename I> void join(ostream &ost, I s, I t, string d=" "){for(auto i=s; i!=t; ++i){if(i!=s)ost<<d; ost<<*i;}ost<<endl;}
template <typename T> istream& operator>>(istream &is, vector<T> &v){for(auto &a : v) is >> a; return is;}
template <typename T, typename U> istream& operator>>(istream &is, pair<T,U> &p){is >> p.first >> p.second; return is;}

template <typename Iter> ostream& out_container(ostream &os, Iter first, Iter last){
  os << "{"; auto itr = first; while(itr != last){if(itr != first) os << ","; os << *itr; ++itr;} os << "}"; return os;
}

template <typename T> ostream& operator<<(ostream &os, const vector<T> &c){return out_container(os,ALL(c));}
template <typename T> ostream& operator<<(ostream &os, const deque<T> &c){return out_container(os,ALL(c));}
template <typename T> ostream& operator<<(ostream &os, const set<T> &c){return out_container(os,ALL(c));}
template <typename T> ostream& operator<<(ostream &os, const unordered_set<T> &c){return out_container(os,ALL(c));}
template <typename T, typename U> ostream& operator<<(ostream &os, const map<T,U> &c){return out_container(os,ALL(c));}
template <typename T, typename U> ostream& operator<<(ostream &os, const unordered_map<T,U> &c){return out_container(os,ALL(c));}
template <typename T, typename U> ostream& operator<<(ostream& os, const pair<T,U> &p){os << "(" << p.first << "," << p.second << ")"; return os;}

template <typename T> T& chmin(T &a, const T &b){return a = min(a,b);}
template <typename T> T& chmax(T &a, const T &b){return a = max(a,b);}


class UnionFind{
  vector<int> _parent, _depth, _size;
public:
  UnionFind(int n): _parent(n), _depth(n,1), _size(n,1){REP(i, n) _parent[i] = i;}
  int root(int i){
    if(_parent[i] == i) return i;
    else return _parent[i] = root(_parent[i]);
  }
  bool same(int i, int j){return root(i) == root(j);}
  int merge(int i, int j){
    int ri = root(i), rj = root(j);
    if(ri == rj) return ri;
    if(ri != rj){
      if(_depth[ri] < _depth[rj]){
	_parent[ri] = rj; _size[rj] += _size[ri];
	return rj;
      }else{
	_parent[rj] = ri; _size[ri] += _size[rj];
	if(_depth[ri] == _depth[rj]) ++_depth[ri];
	return ri;
      }
    }
  }
  int size(int i){return _size[root(i)];}
};


class BipartiteGraph{
  int n;
  UnionFind check;

public:
  BipartiteGraph(int n): n(n), check(2*n){}

  void add_diff(int i, int j){ // iとjを異なる色で塗る。
    check.merge(i,j+n);
    check.merge(i+n,j);
  }

  void add_same(int i, int j){ // iとjを同じ色で塗る。 = iとjを同じ端点と見做す。
    check.merge(i,j);
    check.merge(i+n,j+n);
  }

  bool is_bipartite_graph(int i){ // iを含む連結グラフが二部グラフかを判定する。
    return !check.same(i,i+n);
  }

  bool is_same(int i, int j){ // iとjが同じ色で塗られているか判定する。
    return check.same(i,j);
  }
};


int main(){
  cin.tie(0);
  ios::sync_with_stdio(false);

  LLI N,M;
  while(cin >> N >> M){
    BipartiteGraph bg(N);
    REP(i,M){
      int a,b; cin >> a >> b; --a, --b;
      bg.add_diff(a,b);
    }
    
    if(bg.is_bipartite_graph(0)){
      LLI a=0,b;

      REP(i,N) if(bg.is_same(0,i)) ++a;
      b = N - a;
      
      cout << a*b-M << endl;
    }else{
      cout << N*(N-1)/2-M << endl;
    }
  }
  
  return 0;
}


Measured memory_bytes: 2560