#include <algorithm>
#include <cassert>
#include <cmath>
#include <cstdarg>
#include <cstdio>
#include <cstring>
#include <deque>
#include <iomanip>
#include <iostream>
#include <iterator>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <utility>
#include <vector>

#define whlie while
#define mp make_pair
#define pb push_back
#define fi first
#define se second
#define inf 1001001001
#define mod 1000000007
#define FOR(i,a,b) for(int (i)=((int)a); (i)<((int)b); (i)++) // [a,b)
#define rep(i,N) FOR((i), 0, ((int)N)) // [0,N)
#define FORR(i,a,b) for(int (i)=((int)b) - 1; (i)>=((int)a); (i)--)
#define repr(i,N) FORR((i), 0, ((int)N))
#define all(v) (v).begin(),(v).end()
#define sz(v) ((int)(v).size())
#define vrep(v,it) for(auto it=v.begin();it<v.end();it++)
#define vrepr(v,it) for(auto it=v.rbegin();it<v.rend();it++)
#define inx(t,...) t __VA_ARGS__; in(__VA_ARGS__)
#define mem(ar,val) memset((ar), (val), sizeof(ar) )

// デバッグ用
// dbg(...) printfと同様に使用可能 
// trc(var) (変数名)=(値)と表示
// stopif(val) 条件分が真の時に止まる
// vd(v,N) vの中身を表示

#ifdef LOCAL
    #define dbg(...) fprintf(stderr, __VA_ARGS__)
    #define trc(...) do{cout << #__VA_ARGS__ << " = "; dbg_out(__VA_ARGS__);}while(0)
    #define stopif(val) assert( !(val) )
    #define vdbg(v,...) do{cout << #v << " = "; vector_debug(v , ##__VA_ARGS__);}while(0)
#else
    #define dbg(...) 1
    #define trc(...) 1
    #define stopif(...) 1
    #define vdbg(...) 1
#endif

using namespace std;
typedef long long ll;
typedef pair<int,int> pii;
typedef pair<ll,ll> pll;
typedef vector<int> vi;
typedef vector<ll> vl;
typedef vector<string> vs;
typedef vector<pii> vpii;
typedef vector< vector<int> > vvi;

struct IoSetup {
  IoSetup() {
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    cout << fixed << setprecision(10);
    cerr << fixed << setprecision(10);
  }
} iosetup;

int gcd(int a, int b){if(a>b) swap(a,b); return a==0 ? b : gcd(b%a,a);} ll gcd(ll a, ll b){if(a>b) swap(a,b); return a==0 ? b : gcd(b%a,a);}
int lcm(int a, int b){return (a / gcd(a,b)) * b;} ll lcm(ll a, ll b){return (a / gcd(a,b)) * b;}
inline int pow(int a, int b){int ans = 1; rep(i,b) ans *= a; return ans;} inline ll pow(ll a, ll b){ll ans = 1; rep(i,b) ans*= a; return ans;}
inline ll pow(int a, ll b){ll ans = 1; rep(i,b) ans*= a; return ans;} inline ll pow(ll a, int b){ll ans = 1; rep(i,b) ans*= a; return ans;}
template<typename T, typename U> inline bool amin(T &x, U y) { return (y < x) ? (x = y, true) : false; }
template<typename T, typename U> inline bool amax(T &x, U y) { return (x < y) ? (x = y, true) : false; }
template<typename C> inline void _cin(C &c){cin >> c;}
template<typename T,typename U> inline void _cin(pair<T,U> &p){cin >> p.fi; cin >> p.se;}
template<typename C> inline void _cout(const C &c){cout << c;}
template<typename T,typename U> inline void _cout(const pair<T,U> &p){cout << p.fi << ' ' << p.se;}
void in(){} template <typename T,class... U> void in(T &t,U &...u){ _cin(t); in(u...);}
void out(){cout << endl;} template <typename T,class... U> void out(const T &t,U ...u){ _cout(t); if(sizeof...(u)) cout << ' '; out(u...);}
template<typename C> inline void in(vector<C> &v,int N=-1){if(sz(v) != 0){int M=(N == -1) ? sz(v) : N; rep(i,M) _cin(v[i]);}else{C c;rep(i,N) v.pb((_cin(c),c));}}
template<typename C> inline void in(C v[],int N){rep(i,N) _cin(v[i]);}
template<typename C> inline void out(const vector<C> &v,int N=-1){int M=(N == -1) ? sz(v) : N; rep(i,M) {cout<<( (i)?" ":"" ); _cout(v[i]);} cout<<endl; }
template<typename C> inline void out(C v[],int N){rep(i,N) {cout<<( (i)?" ":"" ); _cout(v[i]);} cout<<endl; }
template<typename C> inline void vector_debug(const vector<C> &v,int N=-1){cout << "{"; int M=(N == -1) ? sz(v) : N; rep(i,M) {cout<<( (i)?", ":"" ); _cout(v[i]);} cout<<"}"; }
template<typename C> inline void vector_debug(C v[], int N){cout << "{"; rep(i,N) {cout<<((i)?", ":""); _cout(*(v+i));} cout<<"}\n";}
void dbg_out(){cout << endl;} template <typename T,class... U> void dbg_out(const T &t,U ...u){ _cout(t); if(sizeof...(u)) cout << ", "; dbg_out(u...);}
template<typename C,class... U> void dbg_out(const vector<C> &v,U ...u){vector_debug(v); if(sizeof...(u)) cout << ", "; dbg_out(u...);}
template<typename C,class... U> void dbg_out(const vector<vector<C>> &v,U ...u){cout << "{ "; rep(i,sz(v)) {if(i)cout<<", "; vector_debug(v[i]);} cout << " }"; if(sizeof...(u)) cout << ", "; dbg_out(u...);}
template<typename C> inline C vmax(const vector<C> &v){C n=v[0]; rep(i,sz(v)) amax(n,v[i]); return n;} template<typename C> inline C vmax(C v[], int N){C n=v[0]; rep( i , N ) amax(n,v[i]); return n;}
template<typename C> inline C vmin(const vector<C> &v){C n=v[0]; rep(i,sz(v)) amin(n,v[i]); return n;} template<typename C> inline C vmin(C v[], int N){C n=v[0]; rep( i , N ) amin(n,v[i]); return n;}
template<typename C> inline C vsum(const vector<C> &v){C n=0; rep(i,sz(v)) n+=v[i]; return n;} template<typename C> inline C vsum(C v[], int N){C n=0; rep( i , N ) n+=v[i]; return n;}

// ini(A,B,C) => int A,B,C; cin >> A >> B >> C; 
// in(A,B,C) => cin >> A >> B >> C;   invi(v,N) =>vi v; rep(i,N) v.pb( (int x,cin >> x,x) );
// out(A,B,C) cout << A << ' ' <<  B << ' ' << C;
// in,outともにベクトル・配列・pairに使用可能(ただしベクトル・配列は１つしか入れられない)
// amax(x,y) bool関数　x<yの時にxにyを代入してtrueを返す

ll N,M; 

// 幅優先探索 1次元ver
constexpr int N_MAX = 100000;
queue<int> Q;
int A[N_MAX + 10]; // 深さを記入する配列
bool bfs(int src, vvi &v){ // v...隣接リスト
    mem(A,-1);
    Q.push(src); // Qの初期化
    A[src] = 0; // A[スタート地点]の深さ
    while(! Q.empty()){
        int cur = Q.front();
        trc(v[cur] , cur);
        Q.pop();
        for(int x : v[cur]){ // 探索範囲
            trc(x,A[x]);
            if(A[x] == -1){ // 条件
                int dst = x;
                trc(dst);
                A[dst]=A[cur]+1; // dstの深さはA[cur]+1
                Q.push(dst); // Qにdstを追加
            }
            else if( (A[cur] + 1) % 2 != A[x] % 2 ){
                return false;
            }
        }
    }
    return true;
}

bool dfs(int src,int depth,vvi &v){
    A[src] = depth;
    for(int x: v[src]){
        if(A[x] != -1){
            if(A[x] == depth){
                out( N * (N - 1L) / 2L - M);
                exit(0);
            }
        }
        else dfs(x, 3 - depth, v);
    }
    return true;
}

int main(){
    in(N,M);
    vvi v(N);
    rep(hoge,M){
        int i,j; in(i,j);
        i--; j--;
        v[i].pb(j); v[j].pb(i);
    }
    mem(A,-1);
    if(!bfs(0,v)){
        out( N * (N - 1L) / 2L - M);
        return 0;
    }
    ll cnt[2] = {};
    rep(i,N){
        if(A[i] % 2 == 1) cnt[0]++;
        else cnt[1]++;
        trc(A[i],i);
    }
    out(cnt[0] * cnt[1] - M);


    
}


Measured memory_bytes: 6272