ABC282D WA

#include <assert.h>
#include <bits/stdc++.h>
using namespace std;
#define dbg(...) logger(#__VA_ARGS__, __VA_ARGS__)
template <typename... Args> void logger(string vars, Args &&... values)
{
    cerr << vars << " = ";
    string delim = "";
    (..., (cerr << delim << values, delim = ", "));
    cerr << endl;
}

template <class T> inline auto vv(int m) { return vector<vector<T>>(m, vector<T>(m)); }
template <class T> inline auto vv(int m, int n) { return vector<vector<T>>(m, vector<T>(n)); }
template <class T, T init> inline auto vv(int m) { return vector<vector<T>>(m, vector<T>(m, init)); }
template <class T, T init> inline auto vv(int m, int n) { return vector<vector<T>>(m, vector<T>(n, init)); }

template <class T> using mpq = priority_queue<T, vector<T>, greater<T>>;
using vi = vector<int>;
using ll = long long;
using pii = pair<int, int>;

vi g[200003];
int color[200003];
int vis[200003];
int cp_cnt[200003];

int coloring(int u, int c, int cp_id)
{
    color[u] = c;
    vis[u] = 1;
    cp_cnt[u] = cp_id;
    int ret = 1;
    for (auto v : g[u]) {
        if (vis[v]) {
            if (c * -1 != color[v]) {
                return 0;
            }
        } else {
            ret = ret & coloring(v, c * -1, cp_id);
        }
    }
    return ret;
}

int main(int argc, char **argv)
{
    int n, m;
    cin >> n >> m;
    int u, v;
    for (int i = 0; i < m; ++i)
        cin >> u >> v, g[u].push_back(v), g[v].push_back(u);

    int cp_id = 1;
    for (int i = 1; i <= n; ++i) {
        if (vis[i] == 0) {
            int bi_par = coloring(i, 1, cp_id);
            if (bi_par == 0) {
                cout << 0 << endl;
                return 0;
            }
        }
    }

    int cnt[2] = {0, 0};
    map<int, array<int, 2>> cp_map;
    for (int i = 1; i <= n; ++i) {
        cnt[(color[i] + 1) / 2]++;
        cp_map[cp_cnt[i]][(color[i] + 1) / 2]++;
    }
    ll ans = 0;
    for (int i = 1; i <= n; ++i) {
        int c = (color[i] + 1) / 2;
        // dbg(c, cnt[1 - c]);
        // ans += cnt[1 - c] - g[i].size();
        ans += cp_map[cp_cnt[i]][1 - c] - g[i].size();
        ans += n - cp_map[cp_cnt[i]][0] - cp_map[cp_cnt[i]][1];
    }
    ans /= 2;
    cout << ans << endl;
    return 0;
};