#include<bits/stdc++.h>

int main(){
    using namespace std;
    unsigned long N, M;
    cin >> N >> M;
    vector<unsigned long> uf(2 * N), sz(2 * N);
    iota(uf.begin(), uf.end(), 0UL);
    fill(sz.begin(), sz.begin() + N, 1);
    const auto& find = [&uf](unsigned long i) -> unsigned long {
        while(i != uf[i])i = uf[i] = uf[uf[i]];
        return i;
    };
    const auto& unite = [&uf, &sz, &find](unsigned long i, unsigned long j) -> unsigned long {
        i = find(i);
        j = find(j);
        if(i == j)return 0;
        if(sz[i] < sz[j])swap(i, j);
        sz[i] += sz[j];
        uf[j] = i;
        return 1;
    };
    const auto& add_edge = [&N, &unite](unsigned long i, unsigned long j) -> void { unite(i, j + N); unite(i + N, j); };
    for(unsigned long i{0}, u, v; i < M; ++i){
        cin >> u >> v;
        add_edge(u - 1, v - 1);
    }
    if(find(0) == find(N))cout << N * (N - 1) / 2 - M << endl;
    else cout << sz[find(0)] * sz[find(N)] - M << endl;
    return 0;
}
#include <bits/stdc++.h>

#define rep(i, n) for (int i = 0; i < int(n); i++)
#define rrep(i, n) for (int i = int(n) - 1; i >= 0; i--)
#define reps(i, n) for (int i = 1; i <= int(n); i++)
#define rreps(i, n) for (int i = int(n); i >= 1; i--)
#define repc(i, n) for (int i = 0; i <= int(n); i++)
#define rrepc(i, n) for (int i = int(n); i >= 0; i--)
#define repi(i, a, b) for (int i = int(a); i < int(b); i++)
#define repic(i, a, b) for (int i = int(a); i <= int(b); i++)
#define each(x, y) for (auto &x : y)
#define all(a) (a).begin(), (a).end()
#define bit32(x) (1 << (x))
#define bit64(x) (1ll << (x))
#define sz(v) ((int) v.size())

using namespace std;

using i64 = long long;
using f80 = long double;
using vi32 = vector<int>;
using vi64 = vector<i64>;
using vf80 = vector<f80>;
using vstr = vector<string>;

inline void yes() { cout << "Yes" << endl; exit(0); }
inline void no() { cout << "No" << endl; exit(0); }
inline i64 gcd(i64 a, i64 b) { if (min(a, b) == 0) return max(a, b); if (a % b == 0) return b; return gcd(b, a % b); }
inline i64 lcm(i64 a, i64 b) { if (min(a, b) == 0) return max(a, b); return a / gcd(a, b) * b; }
template <typename T> class pqasc : public priority_queue<T, vector<T>, greater<T>> {};
template <typename T> class pqdesc : public priority_queue<T, vector<T>, less<T>> {};
template <typename T> inline void amax(T &x, T y) { x = max(x, y); }
template <typename T> inline void amin(T &x, T y) { x = min(x, y); }
template <typename T> inline T exp(T x, i64 n, T e = 1) { T r = e; while (n > 0) { if (n & 1) r *= x; x *= x; n >>= 1; } return r; }
template <typename T> istream& operator>>(istream &is, vector<T> &v) { each(x, v) is >> x; return is; }
template <typename T> ostream& operator<<(ostream &os, vector<T> &v) { rep(i, v.size()) { if (i) os << ' '; os << v[i]; } return os; }
void solve(); int main() { ios::sync_with_stdio(0); cin.tie(0); cout << fixed << setprecision(16); solve(); return 0; }

void solve() {
  int n, m;
  cin >> n >> m;
  vector<vi32> g(n);
  rep(i, m) {
    int u, v;
    cin >> u >> v;
    u--, v--;
    g[u].emplace_back(v);
    g[v].emplace_back(u);
  }
  vi32 dist(n, 1e9);
  auto dfs = [&](auto dfs, int u, int d) -> bool {
    if (dist[u] != 1e9) {
      return dist[u] % 2 == d % 2;
    }
    dist[u] = d;
    for (auto v : g[u]) {
      if (!dfs(dfs, v, d + 1)) return false;
    }
    return true;
  };
  if (dfs(dfs, 0, 0)) {
    int a = 0;
    rep(i, n) a += dist[i] % 2 == 0;
    int b = n - a;
    cout << (i64) a * b - m << endl;
  } else {
    cout << (i64) n * (n - 1) / 2 - m << endl;
  }
}