#include <iostream>
#include <cmath>
#include <functional>
#include <algorithm>
#include <string>
#include <vector>
#include <map>
#include <queue>
#include <tuple>
using namespace std;
long long n, m, a[100009], b[100009], col[100009], g[100009], cnt; vector<long long>x[100009];
void dfs(int pos) {
	if (col[pos] >= 1)return;
	col[pos] = cnt; g[cnt]++;
	for (int i = 0; i < x[pos].size(); i++)dfs(x[pos][i]);
}
int main() {
	cin >> n >> m;
	for (int i = 0; i < m; i++) {
		cin >> a[i] >> b[i]; x[a[i]].push_back(b[i]); x[b[i]].push_back(a[i]);
	}
	for (int i = 1; i <= n; i++) {
		if (col[i] == 0) { cnt++; dfs(i); }
	}
	long long W1 = n - g[col[1]], X1 = W1*(W1 - 1) / 2LL;
	for (int i = 0; i < m; i++) {
		if (col[a[i]] != col[1])X1--;
	}
	X1 += g[col[1]] * (g[col[1]] - 1) / 2;
	for (int i = 0; i < m; i++) {
		if (col[a[i]] == col[1])X1--;
	}

	long long W2 = n - g[col[2]], X2 = W2*(W2 - 1) / 2LL;
	for (int i = 0; i < m; i++) {
		if (col[a[i]] != col[2])X2--;
	}
	X2 += g[col[2]] * (g[col[2]] - 1) / 2;
	for (int i = 0; i < m; i++) {
		if (col[a[i]] == col[2])X2--;
	}
	cout << max(X1, X2) << endl;
	return 0;
}