Submission #69074682

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Source Code Expand

#include<bits/stdc++.h>
using namespace std;
#define rep(i, s, t) for(int i = (s); i <= (t); i ++)
#define per(i, s, t) for(int i = (s); i >= (t); i --)
template<typename T, typename T2>
inline void chmin(T &x, T2 &&y) { x = min(x, y); }
template<typename T, typename T2>
inline void chmax(T &x, T2 &&y) { x = max(x, y); }
typedef long long ll;

const int N = 2e5 + 5;
int d[N], n, m;

signed main()
{
    ios::sync_with_stdio(0);cin.tie(0);
    cin >> n >> m;
    rep(i, 1, m)
    {
        int x, y; cin >> x >> y;
        d[x] ++, d[y] ++;
    }
    int cnt = 0;
    ll ans = 1ll * n * (n - 1) / 2;
    rep(i, 1, n)
    {
        if((n - 1 - d[i]) & 1)
            cnt ++, ans --;
    }
    // cerr << cnt << endl;
    assert(cnt % 2 == 0);
    ans += cnt / 2;
    cout << ans;

    return 0;
}

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