#include <bits/stdc++.h>
using namespace std;
#define int long long
//TEMPLATE START---------------8<---------------8<---------------8<---------------8<---------------//
typedef long long ll;       typedef long double ld;  typedef pair<int,int> pii; typedef pair<ll,ll> pll;  typedef vector<int> vi;   typedef vector<ll> vl;
typedef vector<string> vst; typedef vector<bool> vb; typedef vector<ld> vld;    typedef vector<pii> vpii; typedef vector<pll> vpll; typedef vector<vector<int> > vvi;
const int INF = (0x7FFFFFFFL); const ll INFF = (0x7FFFFFFFFFFFFFFFL); const string ALPHABET = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
const int MOD = 1e9 + 7;       const int MODD = 998244353;            const string alphabet = "abcdefghijklmnopqrstuvwxyz";
const double PI = acos(-1.0);  const double EPS = 1e-9;               const string Alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";
int dx[9] = { 1, 0, -1,  0,  1, -1, -1, 1, 0 };
int dy[9] = { 0, 1,  0, -1, -1, -1,  1, 1, 0 };
#define ln '\n'
#define scnaf scanf
#define sacnf scanf
#define sancf scanf
#define SS(type, ...)type __VA_ARGS__;MACRO_VAR_Scan(__VA_ARGS__);
template<typename T> void MACRO_VAR_Scan(T& t){cin >> t;}template<typename First, typename...Rest> void MACRO_VAR_Scan(First& first, Rest&...rest){cin >> first;MACRO_VAR_Scan(rest...);}
#define SV(type,c,n) vector<type> c(n);for(auto& i:c)cin >> i;
#define SVV(type,c,n,m) vector<vector<type>> c(n,vector<type>(m));for(auto& r:c)for(auto& i:r)cin >> i;
template<class T,class U>ostream &operator<<(ostream &o,const pair<T,U>&j){o<<"{"<<j.first<<", "<<j.second<<"}";return o;}
template<class T,class U>ostream &operator<<(ostream &o,const map<T,U>&j){o<<"{";for(auto t=j.begin();t!=j.end();++t)o<<(t!=j.begin()?", ":"")<<*t;o<<"}";return o;}
template<class T>ostream &operator<<(ostream &o,const set<T>&j){o<<"{";for(auto t=j.begin();t!=j.end();++t)o<<(t!=j.begin()?", ":"")<<*t;o<<"}";return o;}
template<class T>ostream &operator<<(ostream &o,const vector<T>&j){o<<"{";for(int i=0;i<(int)j.size();++i)o<<(i>0?", ":"")<<j[i];o<<"}";return o;}
inline int print(void){cout << endl; return 0;}
template<class Head> int print(Head&& head){cout << head;print();return 0;} template<class Head,class... Tail> int print(Head&& head,Tail&&... tail){cout<<head<<" ";print(forward<Tail>(tail)...);return 0;}
inline int debug(void){cerr << endl; return 0;}
template<class Head> int debug(Head&& head){cerr << head;debug();return 0;} template<class Head,class... Tail> int debug(Head&& head,Tail&&... tail){cerr<<head<<" ";debug(forward<Tail>(tail)...);return 0;}
template<typename T> void PA(T &a){int ASIZE=sizeof(a)/sizeof(a[0]);for(int ii=0;ii<ASIZE;++ii){cout<<a[ii]<<" \n"[ii==ASIZE-1];}}
template<typename T> void PV(T &v){int VSIZE=v.size();for(int ii=0;ii<VSIZE;++ii){cout<<v[ii]<<" \n"[ii==VSIZE-1];}}
#define ER(x)  cerr << #x << " = " << (x) << endl;
#define ERV(v) {cerr << #v << " : ";for(const auto& xxx : v){cerr << xxx << " ";}cerr << "\n";}
inline int YES(bool x){cout<<((x)?"YES":"NO")<<endl;return 0;} inline int Yes(bool x){cout<<((x)?"Yes":"No")<<endl;return 0;}  inline int yes(bool x){cout<<((x)?"yes":"no")<<endl;return 0;}
inline int yES(bool x){cout<<((x)?"yES":"nO")<<endl;return 0;} inline int Yay(bool x){cout<<((x)?"Yay!":":(")<<endl;return 0;}
template<typename A,typename B> void sankou(bool x,A a,B b){cout<<((x)?(a):(b))<<endl;}
#define _overload3(_1,_2,_3,name,...) name
#define _REP(i,n) REPI(i,0,n)
#define REPI(i,a,b) for(ll i=ll(a);i<ll(b);++i)
#define REP(...) _overload3(__VA_ARGS__,REPI,_REP,)(__VA_ARGS__)
#define _RREP(i,n) RREPI(i,n,0)
#define RREPI(i,a,b) for(ll i=ll(a);i>=ll(b);--i)
#define RREP(...) _overload3(__VA_ARGS__,RREPI,_RREP,)(__VA_ARGS__)
#define EACH(e,v) for(auto& e : v)
#define PERM(v) sort((v).begin(),(v).end());for(bool c##p=1;c##p;c##p=next_permutation((v).begin(),(v).end()))
#define ADD(a,b) a=(a+ll(b))%MOD
#define MUL(a,b) a=(a*ll(b))%MOD
inline ll MOP(ll x,ll n,ll m=MOD){ll r=1;while(n>0){if(n&1)(r*=x)%=m;(x*=x)%=m;n>>=1;}return r;}
inline ll gcd(ll a,ll b){return b?gcd(b,a%b):a;}inline ll lcm(ll a,ll b){return a*b/gcd(a,b);}inline ll POW(ll a,ll b){ll c=1ll;do{if(b&1)c*=1ll*a;a*=1ll*a;}while(b>>=1);return c;}
template<typename T,typename A,typename B> inline bool between(T x,A a,B b) {return ((a<=x)&&(x<b));}template<class T> inline T sqr(T x){return x*x;}
template<typename A,typename B> inline bool chmax(A &a,const B &b){if(a<b){a=b;return 1;}return 0;}
template<typename A,typename B> inline bool chmin(A &a,const B &b){if(a>b){a=b;return 1;}return 0;}
#define tmax(x,y,z) max((x),max((y),(z)))
#define tmin(x,y,z) min((x),min((y),(z)))
#define PB push_back
#define MP make_pair
#define MT make_tuple
#define all(v) (v).begin(),(v).end()
#define rall(v) (v).rbegin(),(v).rend()
#define SORT(v) sort((v).begin(),(v).end())
#define RSORT(v) sort((v).rbegin(),(v).rend())
#define EXIST(s,e) (find((s).begin(),(s).end(),(e))!=(s).end())
#define EXISTST(s,c) (((s).find(c))!=string::npos)
#define POSL(x,val) (lower_bound(x.begin(),x.end(),val)-x.begin())
#define POSU(x,val) (upper_bound(x.begin(),x.end(),val)-x.begin())
#define GEQ(x,val) (int)(x).size() - POSL((x),(val))
#define GREATER(x,val) (int)(x).size() - POSU((x),(val))
#define LEQ(x,val) POSU((x),(val))
#define LESS(x,val) POSL((x),(val))
#define SZV(a) int((a).size())
#define SZA(a) sizeof(a)/sizeof(a[0])
#define ZERO(a) memset(a,0,sizeof(a))
#define MINUS(a) memset(a,0xff,sizeof(a))
#define MEMINF(a) memset(a,0x3f,sizeof(a))
#define FILL(a,b) memset(a,b,sizeof(a))
#define UNIQUE(v) sort((v).begin(),(v).end());(v).erase(unique((v).begin(),(v).end()),(v).end())
struct abracadabra{
  abracadabra(){
    cin.tie(0); ios::sync_with_stdio(0);
    cout << fixed << setprecision(20);
    cerr << fixed << setprecision(5);
  };
} ABRACADABRA;

//TEMPLATE END---------------8<---------------8<---------------8<---------------8<---------------//

/*
・グラフ
  > Dijkstra
  > BellmanFord
  > Warshall-Floyd
  > Kruskal
[応用] 単一終点最短路問題は, すべての有向辺を逆向きに張り替えると, 単一始点最短路問題に帰着できる.
[使用例]
Graph<int> g(N);              // 頂点数N, 重さの型がintのグラフを宣言
add_edge(g,a,b,c);            // グラフgに, aからbへの重さcの無向辺を追加
add_arc(g,a,b,c);             // グラフgに, aからbへの重さcの有向辺を追加
add_to_edges(edges,a,b,c);    // 辺集合edgesに, 始点a, 終点b, 重さcの辺を追加
*/

template<typename T> struct Edge {
  int from, to;
  T weight;
  Edge() : from(0), to(0), weight(0) {}
  Edge(int f, int t, T w) : from(f), to(t), weight(w) {}
};
template<typename T> using Edges = vector< Edge< T > >;
template<typename T> using Graph = vector< Edges< T > >;
template<typename T> void     add_edge(Graph< T > &g, int from, int to, T w = 1) { g[from].emplace_back(from,to,w); g[to].emplace_back(to,from,w); }
template<typename T> void      add_arc(Graph< T > &g, int from, int to, T w = 1) { g[from].emplace_back(from,to,w); }
template<typename T> void add_to_edges(Edges< T > &e, int from, int to, T w = 1) { e.emplace_back(from,to,w); }

/*
・二部グラフの判定
  > O(E+V) [E:辺の数, V:頂点の数]
[備考] 二部グラフならTrueを返す.
[使用例] isBipartiteGraph(g);
[その他] 二部グラフだった際に, 片方の集合の大きさが知りたい場合は, return retを削除して, intを返すようにする.
        その場合は, 二部グラフならばその集合の大きさを, そうでない場合は-1を返す.
*/

template <typename T> int isBipartiteGraph(const Graph<T> &g) {
  int V = g.size();
  vector<int> color(V, 0);
  bool ret = true;
  function<void(int, int)> dfs = [&](int i, int clr) {
    if (color[i] != 0) return;
    color[i] = clr;
    for (auto& e: g[i]) {
      if (color[e.to] == 0) dfs(e.to, -clr);
      else if (color[e.to] == clr) ret = false;
    }
  };
  dfs(0, 1);
  // return ret;
  int cnt = 0;
  for (auto& e: color) if (e == 1) ++cnt;
  return !ret ? -1 : cnt;
}

/*
・二部グラフの最大マッチング
  > O(EV) [E:辺の数, V:頂点の数]
[備考] 最大流のアルゴリズムを用いて求める.
[応用] 最大マッチングは, 最小点被覆と一致(Mとおく).
      最大安定集合(最大独立集合)は, 最小辺被覆と(V-M)で一致.
[参考] https://qiita.com/drken/items/e805e3f514acceb87602
      https://qiita.com/drken/items/7f98315b56c95a6181a4
[使用例]
Bipartite_Matching bip(N);      // 頂点数Nのグラフを用意.
bip.add_edge(from, to);         // 頂点fromから頂点toへの有向辺を足す.
bip.bipartite_matching();       // 最大マッチングを求める.
*/

struct Bipartite_Matching {
  vector< vector< int > > graph;
  vector< int > match, alive, used;
  int timestamp;

  Bipartite_Matching(int n) : timestamp(0) {
    graph.resize(n);
    alive.assign(n, 1);
    used.assign(n, 0);
    match.assign(n, -1);
  }

  void add_edge(int u, int v) {
    graph[u].push_back(v);
    graph[v].push_back(u);
  }

  bool dfs(int v) {
    used[v] = timestamp;
    for (int i = 0; i < graph[v].size(); i++) {
      int u = graph[v][i], w = match[u];
      if (alive[u] == 0) continue;
      if (w == -1 || (used[w] != timestamp && dfs(w))) {
        match[v] = u;
        match[u] = v;
        return true;
      }
    }
    return false;
  }

  int bipartite_matching() {
    int ret = 0;
    for (int i = 0; i < graph.size(); i++) {
      if (alive[i] == 0) continue;
      if (match[i] == -1) {
        ++timestamp;
        ret += dfs(i);
      }
    }
    return ret;
  }
};

signed main() {

  SS(int, N, M);

  Graph<int> g(N);
  Bipartite_Matching bip(N);

  REP(i, M) {
    SS(int, A, B);
    --A, --B;
    bip.add_edge(A, B);
    add_edge(g, A, B);
  }

  int isbg = isBipartiteGraph(g);
  int res = 0;
  if (isbg == -1) res = N * (N - 1) / 2 - M;
  else res = isbg * (N - isbg) - M;

  cout << max<ll>(res, 0) << endl;

}


Measured memory_bytes: 19072