ABC282D.cpp

/*
 * @FilePath: \c++\ABC282D.cpp
 * @Author: WRT_Partisan
 * @Date: 2025-12-13 14:27:50
 */
#include <bits/stdc++.h>
using namespace std;
#define int long long
int n, m, u, v, c[200005], w, b, ans, s;
bool book[200005];
vector<int> mp[200005];
void dfs(int x, int co)
{
    book[x] = 1, c[x] = co, (co ? b : w)++;
    for (auto i : mp[x])
    {
        if (book[i] && c[i] == c[x])
            cout << 0, exit(0);
        else if (!book[i])
            dfs(i, !co);
    }
}
signed main()
{
    cin.tie(0)->sync_with_stdio(0);
    cin >> n >> m;
    for (int i = 1; i <= m; i++)
        cin >> u >> v, mp[u].push_back(v), mp[v].push_back(u);
    for (int i = 1; i <= n; i++)
        if (!book[i])
            w = b = 0, dfs(i, 0), ans += w * b, s += (w + b) * (n - w - b);
    cout << ans - m + s / 2;
    return 0;
}