int main() {
	cin.tie(nullptr)->sync_with_stdio(false);

	auto solve = [&]() {
		int n, m;
		cin >> n >> m;

		vector adj(n, vector<int>(n));
		while (m--) {
			int u, v;
			cin >> u >> v;
			u--, v--;
			adj[u][v] = adj[v][u] = true;
		}

		vector<int> col(n, -1);
		vector<int> dp(n + 1);
		dp[0] = true;

		for (int i = 0; i < n; i++) {
			if (col[i] != -1) {
				continue;
			}
			vector<int> q{i};
			col[i] = 0;
			for (int j = 0; j < int(q.size()); j++) {
				int u = q[j];
				for (int v = 0; v < n; v++) {
					if (u == v || adj[u][v]) {
						continue;
					}
					if (col[v] == -1) {
						q.push_back(v);
						col[v] = col[u] ^ 1;
					} else if (col[u] == col[v]) {
						cout << "-1\n";
						return;
					}
				}
			}
			int c0 = count_if(q.begin(), q.end(), [&](auto u) { return col[u] == 0; });
			int c1 = q.size() - c0;
			vector<int> ndp(n + 1);
			for (int i = n; i >= 0; i--) {
				if (i >= c0) {
					ndp[i] |= dp[i - c0];
				}
				if (i >= c1) {
					ndp[i] |= dp[i - c1];
				}
			}
			dp = move(ndp);
		}

		for (int i = n / 2; i >= 0; i--) {
			if (dp[i]) {
				cout << n - 2 * i << '\n';
				return;
			}
		}
	};

	solve();
}

answer.code: In function ‘int main()’:
answer.code:2:9: error: ‘cin’ was not declared in this scope
    2 |         cin.tie(nullptr)->sync_with_stdio(false);
      |         ^~~
answer.code: In lambda function:
answer.code:8:17: error: ‘vector’ was not declared in this scope
    8 |                 vector adj(n, vector<int>(n));
      |                 ^~~~~~
answer.code:13:25: error: ‘adj’ was not declared in this scope
   13 |                         adj[u][v] = adj[v][u] = true;
      |                         ^~~
answer.code:16:24: error: expected primary-expression before ‘int’
   16 |                 vector<int> col(n, -1);
      |                        ^~~
answer.code:17:24: error: expected primary-expression before ‘int’
   17 |                 vector<int> dp(n + 1);
      |                        ^~~
answer.code:18:17: error: ‘dp’ was not declared in this scope
   18 |                 dp[0] = true;
      |                 ^~
answer.code:21:29: error: ‘col’ was not declared in this scope
   21 |                         if (col[i] != -1) {
      |                             ^~~
answer.code:24:32: error: expected primary-expression before ‘int’
   24 |                         vector<int> q{i};
      |                                ^~~
answer.code:25:25: error: ‘col’ was not declared in this scope
   25 |                         col[i] = 0;
      |                         ^~~
answer.code:26:49: error: ‘q’ was not declared in this scope
   26 |                         for (int j = 0; j < int(q.size()); j++) {
      |                                                 ^
answer.code:29:55: error: ‘adj’ was not declared in this scope
   29 |                                         if (u == v || adj[u][v]) {
      |                                                       ^~~
answer.code:36:49: error: ‘cout’ was not declared in this scope
   36 |                                                 cout << "-1\n";
      |                                                 ^~~~
answer.code:41:43: error: ‘q’ was not declared in this scope
   41 |                         int c0 = count_if(q.begin(), q.end(), [&](auto u) { return col[u] == 0; });
      |                                           ^
answer.code:41:34: error: ‘count_if’ was not declared in this scope
   41 |                         int c0 = count_if(q.begin(), q.end(), [&](auto u) { return col[u] == 0; });
      |                                  ^~~~~~~~
answer.code:43:32: error: expected primary-expression before ‘int’
   43 |                         vector<int> ndp(n + 1);
      |                                ^~~
answer.code:46:41: error: ‘ndp’ was not declared in this scope
   46 |                                         ndp[i] |= dp[i - c0];
      |                                         ^~~
answer.code:49:41: error: ‘ndp’ was not declared in this scope
   49 |                                         ndp[i] |= dp[i - c1];
      |                                         ^~~
answer.code:52:35: error: ‘ndp’ was not declared in this scope
   52 |                         dp = move(ndp);
      |                                   ^~~
answer.code:52:30: error: ‘move’ was not declared in this scope
   52 |                         dp = move(ndp);
      |                              ^~~~
answer.code:57:33: error: ‘cout’ was not declared in this scope
   57 |                                 cout << n - 2 * i << '\n';
      |                                 ^~~~