https://www.luogu.com.cn/problem/P1330

#include <bits/stdc++.h>
using namespace std;
const int M = 2e5 + 5;
int a[M], vis[M], color[M], ans, anss;
vector<int> f[M];

void dfss(int now)
{
    vis[now] = color[now] = 0;
    for (auto x : f[now])
        if (vis[x])
            dfss(x);
}

bool dfs(int now)
{
    vis[now] = 1;
    if (color[now])
        ans++;
    for (auto x : f[now])
        if (!vis[x])
        {
            color[x] = 1 - color[now];
            if (!dfs(x))
                return 0;
        }
        else if (color[now] == color[x])
            return 0;
    return 1;
}

void solve()
{
    int n, m, x, y;
    cin >> n >> m;
    while (m--)
    {
        cin >> x >> y;
        f[x].push_back(y);
        f[y].push_back(x);
    }
    for (int i = 1; i <= n; ++i)
        if (!vis[i])
        {
            int cnt = 1e9;
            ans = 0;
            if (dfs(i))
                cnt = min(cnt, ans);
            ans = 0;
            dfss(i);
            color[i] = 1;
            if (dfs(i))
                cnt = min(cnt, ans);
            if (cnt == 1e9)
            {
                cout << "Impossible";
                return;
            }
            anss += cnt;
        }
    cout << anss;
}

signed main()
{
    ios::sync_with_stdio(false), cin.tie(0), cout.tie(0);
    int t = 1;
    // cin>>t;
    while (t--)
        solve();
    return 0;
}