#include <bits/stdc++.h>
using namespace std;

using ull = unsigned long long;
using ll = long long;
#define endl "\n"

#define REP(i, n) for (ll i = 0; i < n; i++)
#define REPR(i, n) for (ll i = n; i >= 0; i--)
#define FOR(i, m, n) for (ll i = m; i < n; i++)
#define even(x) (x) % 2 == 0
#define odd(x) (x) % 2 != 0
#define all(x) x.begin(), x.end()
#define rall(x) x.rbegin(), x.rend()
#define pcnt __builtin_popcount
#define buli(x) __builtin_popcountll(x)
#define UNIQUE(v) v.erase(unique(v.begin(), v.end()), v.end());
#define inp(t, x) t x;cin>>x;
#define ithBit(n, i) ((n)>>(i) & 1)
#define INIT() cin.tie(0);ios::sync_with_stdio(0);cout<<fixed<<setprecision(20)

// these functions return the position of result of Binary Search.
#define LB(s, t, x) (int)(lower_bound(s, t, x) - s)
#define UB(s, t, x) (int)(upper_bound(s, t, x) - s)

namespace {
    #define M_PI 3.14159265358979323846
    ll qp(ll a, ll b, int mo)
    {
        ll ans = 1;
        do
        {
            if (b & 1)
                ans = 1ll * ans * a % mo;
            a = 1ll * a * a % mo;
        } while (b >>= 1);
        return ans;
    }
    ll gcd(ll a, ll b) { return b ? gcd(b, a % b) : a; }
    ll lcm(ll a, ll b)
    {
        ll temp = gcd(a, b);
        return temp ? (a / temp * b) : 0;
    }
    int mDays[] = {31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
    int dx[4] = {1, 0, -1, 0}, dy[4] = {0, 1, 0, -1};
    int dx8[] = {1, -1, 0, 0, 1, 1, -1, -1}, dy8[] = {0, 0, -1, 1, -1, 1, -1, 1};

    template <typename F>
    class
    #if defined(__has_cpp_attribute) && __has_cpp_attribute(nodiscard)
        [[nodiscard]]
    #elif defined(__GNUC__) && __GNUC_PREREQ(3, 4)
        __attribute__((warn_unused_result))
    #endif // defined(__has_cpp_attribute) && __has_cpp_attribute(nodiscard)
        FixPoint : F {
            public :
                explicit constexpr FixPoint(F &&f) noexcept : F(std::forward<F>(f)) {}

            template <typename... Args>
            constexpr decltype(auto)
            operator()(Args &&... args) const {
                return F::operator()(*this, std::forward<Args>(args)...);
    } // namespace
    }
    ; // class FixPoint
    template <typename F>
    static inline constexpr decltype(auto)
    makeFixPoint(F &&f) noexcept
    {
        return FixPoint<F>{std::forward<F>(f)};
    }

    template <typename T>
    vector<T> make_v(size_t a) { return vector<T>(a); }
    template <typename T, typename... Ts>
    auto make_v(size_t a, size_t b, Ts... ts) { return vector<decltype(make_v<T>(b, ts...))>(a, make_v<T>(b, ts...)); }
    template <typename T, typename V>
    typename enable_if<is_class<T>::value == 0>::type
    fill_v(T &t, const V &v) { t = v; }
    template <typename T, typename V>
    typename enable_if<is_class<T>::value != 0>::type
    fill_v(T &t, const V &v) { for (auto &e : t) fill_v(e, v); }

    template <class T>
    bool chmax(T &a, const T &b) { if (a < b) { a = b; return 1; } return 0; }
    template <class T>
    bool chmin(T &a, const T &b) { if (b < a) { a = b; return 1; } return 0; }

    inline bool rangeCheck2D(int nx, int ny, int Width, int Height) { return nx >= 0 and nx < Width and ny >= 0 and ny < Height; }
    
    ll i_query(ll x)
    {
        cout << "> " << x << endl;
        fflush(stdout);
        ll ret;
        cin >> ret;
        return ret;
    }
    ll i_query_2(ll i)
    {
        cout << "? " << i << endl;
        fflush(stdout);
        ll ret;
        cin >> ret;
        return ret;
    }
    void i_answer(ll ans, ll d)
    {
        cout << "! " << ans << " " << d << endl;
        fflush(stdout);
    }
} // namespace

namespace {
    #define DUMPOUT cerr 
    #ifndef DEBUG_
    #define dump(...)
    #else
    #define dump(...) DUMPOUT<<"  "; \
    DUMPOUT<<#__VA_ARGS__<<" :["<<__LINE__<<":"<<__FUNCTION__<<"]"<<endl; \
    DUMPOUT<<"    "; \
    dump_func(__VA_ARGS__)
    #endif 
    void dump_func() { DUMPOUT << endl; }
    template <class Head, class... Tail>
    void dump_func(Head&& head, Tail&&... tail)
    {
        DUMPOUT << head;
        if (sizeof...(Tail) == 0) {
            DUMPOUT << " ";
        }
        else {
            DUMPOUT << ", ";
        }
        dump_func(std::move(tail)...);
    }
    template <class T>
    ostream &operator<<(ostream &os, const vector<T> &v)
    {
        for (auto i = begin(v); i != end(v); ++i)
            os << *i << (i == end(v) - 1 ? "" : " ");
        return os;
    }
    template <class T>
    void out2Dvector(vector<T> v) {
        for (const auto& vv : v)
            cout << vv << endl;
    }
    template <class T>
    istream &operator>>(istream &is, vector<T> &v)
    {
        for (auto i = begin(v); i != end(v); ++i)
            is >> *i;
        return is;
    }
    template<typename T, typename U>
    ostream& operator << (ostream& os, pair<T, U>& pair_var) {
        os << "(" << pair_var.first << ", " << pair_var.second << ")";
        return os;
    }
    template<typename T, typename U>
    ostream& operator << (ostream& os, map<T, U>& map_var) {
        os << "{";
        for (auto itr = map_var.begin(); itr != map_var.end(); itr++) {
            os << "(" << itr->first << ", " << itr->second << ")";
            itr++;
            if(itr != map_var.end()) os << ", ";
            itr--;
        }
        os << "}";
        return os;
    }
    template<typename T>
    ostream& operator << (ostream& os, set<T>& set_var) {
        os << "{";
        for (auto itr = set_var.begin(); itr != set_var.end(); itr++) {
            os << *itr;
            ++itr;
            if(itr != set_var.end()) os << ", ";
            itr--;
        }
        os << "}";
        return os;
    }
}

/*
    lambda expression
    auto f = [](int arg1, double arg2) { return ret; };
    lambda recursion
    auto result = makeFixPoint([&](auto rec, int pos, int v) -> int {
        rec(pos, v);
    })(0, 1);
    auto func = makeFixPoint([]() -> int {});
    int ret = func();

    tuple binding
    auto [x, y] = make_tuple(0, 0);
    for pair
    auto [a, b] = pair<int, int>({v1, v2});

    bitset<N> bs(ini_val); // N must be constant
    bs.reset(); // reset all
*/

class ListG {
public:
    // there's directed edge between A and B
    // if to[A] has element B
    vector<vector<int>> to; 

    map<pair<int, int>, ll> cost;
    void setCost(int u, int v, ll c) { 
        cost[{min(u, v), max(u, v)}] = c;
    }
    ll getCost(int u, int v) {
        return cost[{min(u, v), max(u, v)}];
    }

    ListG(int s) : root(-1) {
        size = s;
        to = make_v<vector<int>>(size);
    }

    void setDirectedEdge(int f, int t) {
        to[f].push_back(t);
    }
    void setIndirectedEdge(int v1, int v2) {
        setDirectedEdge(v1, v2);
        setDirectedEdge(v2, v1);
    }

    void readGraph(int edgeNum, bool directed = false) {
        REP(i, edgeNum) {
            int u, v; cin >> u >> v; u--, v--;
            if (directed)
                setDirectedEdge(u, v);
            else
                setIndirectedEdge(u, v);
        }
    }

    void dfs(vector<char> &visiting, vector<char> &visited, int current, vector<vector<int>> &cloop) {
        for (auto&& next : to[current]) {
            if (visited[next]) continue;
            if (visiting[next]) {
                cloop[current].push_back(next);
                visited[next] = 1;
                dfs(visiting, visited, next, cloop);
                visited[next] = 0;
            } else {
                visiting[next] = 1;
                dfs(visiting, visited, next, cloop);
                visiting[next] = 0;
            }
        }
    }

    // return max depth
    int makeTree(int r) {
        root = r;
        p = make_v<int>(size);
        p[root] = -1;
        depth = make_v<int>(size);
        int maxDepth = 0;
        makeFixPoint([&](auto rec, int c, int d) -> void {
            depth[c] = d;
            chmax(maxDepth, d);
            REP(i, to[c].size()) {
                int next = to[c][i];
                if (p[c] == next) continue;
                p[next] = c;
                rec(next, d + 1);
            }
        })(root, 0);
        // count leaf node
        auto idxs = make_v<int>(size);
        iota(all(idxs), 0);
        leaf_idx = set<int>(all(idxs));
        REP(i, size) {
            if (i == root) continue;
            leaf_idx.erase(p[i]);
        }
        return maxDepth;
    }

    pair<int, int> isBipartite() {
        auto color = make_v<int>(size);
        fill_v(color, 0);

        auto rec = makeFixPoint([&](auto rec, int v, int c) -> bool {
            color[v] = c;
            for (const auto& next : to[v]) {
                if (color[next] == c)
                    return false;
                if (color[next] == 0 and not rec(next, -c))
                    return false;
            }
            return true;
        });

        pair<int, int> ret = {-1, -1};
        REP(i, size) {
            if (color[i] == 0)
                if (not rec(i, 1))
                    return ret;
        }
        ret = {0, 0};
        REP(i, size) {
            if (color[i] > 0) ret.first++;
            else ret.second++;
        }
        return ret;
    }

    void makeEulerTour() {
        assert(root >= 0);
        et_begin = make_v<int>(size);
        et_end = make_v<int>(size);
        tmp_k = 0;
        etdfs(root, -1);
    }

    vector<vector<int>> children() {
        assert(root >= 0);
        auto ret = make_v<vector<int>>(size);
        REP(i, size) {
            int prt = p[i];
            if (prt == -1) continue;
            ret[prt].push_back(i);
        }
        return ret;
    }

    int stronglyConnectedConponent() {
        auto rto = make_v<vector<int>>(size);
        REP(from, size) {
            for (auto&& t : to[from])
                rto[t].push_back(from);
        }
        auto cmp = make_v<int>(size);
        fill_v(cmp, 0);
        auto used = make_v<char>(size);
        fill_v(used, 0);
        vector<int> rets; // return index in order
        REP(i, size) {
            makeFixPoint([&](auto dfs, int v) -> void {
                if (used[v]) return;
                used[v] = 1;
                for (auto&& t : to[v])
                    dfs(t);
                rets.push_back(v);
            })(i);
        }
        fill_v(used, 0);
        int ret = 0;
        REPR(i, rets.size()-1) {
            makeFixPoint([&](auto rdfs, int v, int k) -> void {
                if (used[v]) return;
                used[v] = 1;
                cmp[v] = k;
                for (auto&& rt : rto[v])
                        rdfs(rt, k);
                
                rets.push_back(v);
            })(rets[i], ret++);
        }
        return ret;
    }

    vector<int> topologicalSorted() {
        vector<int> ret;
        auto used = make_v<char>(size);
        fill_v(used, 0);
        REP(i, size) {
            makeFixPoint([&](auto dfs, int v) -> void {
                if (used[v]) return;
                used[v] = 1;
                for (auto&& t : to[v]) 
                    dfs(t);
                ret.push_back(v);
            })(i);
        }
        reverse(all(ret));
        return ret;
    }

    void dfsTree(ListG& dfst) {
        auto visited = make_v<char>(size);
        auto prt = make_v<int>(size);
        fill_v(visited, 0);
        fill_v(prt, 0);
        stack<int> st;
        st.push(0);
        while (st.size()) {
            int c = st.top(); st.pop();
            if (visited[c]) continue;
            visited[c] = 1;
            if (c != 0) dfst.setIndirectedEdge(c, prt[c]);
            for (const auto& next : to[c]) {
                prt[next] = c;
                st.push(next);
            }
        }
    }

    int size, root;
    vector<int> p; // parent for each node. parent of root = -1
    vector<int> depth; // for each node. depth of root node = 0
    vector<int> euler_tour;
    vector<int> et_begin, et_end;
    set<int> leaf_idx;

    int tmp_k;
private:
    void etdfs(int vidx, int pidx) {
        et_begin[vidx] = tmp_k;
        euler_tour.push_back(vidx);
        tmp_k++;
        REP(i, to[vidx].size()) {
            if (to[vidx][i] != pidx) {
                etdfs(to[vidx][i], vidx);
                euler_tour.push_back(vidx);
                tmp_k++;
            }
        }
        et_end[vidx] = tmp_k;
    }
};

int main(void)
{
    INIT(); // comment out for Interective Program

    inp(ll, N); inp(ll, M);
    ListG lg(N);
    lg.readGraph(M);

    auto ret = lg.isBipartite();
    if (ret.first == -1) cout << N * (N - 1) / 2 - M << endl;
    else cout << (ll)ret.first * (ll)ret.second - M << endl;

    return 0;
}
//*/

Measured memory_bytes: 6400