#include <bits/stdc++.h>
using namespace std;
double dp[2004][2004];
map<int, int> l, r;
int main() {
  int n, m;
  cin >> n >> m;
  while (m--) {
    int u, v;
    cin >> u >> v;
    l[u] = 1;
    r[v] = 1;
  }
  for (int i = 1; i <= n; i++) {
    dp[0][i] = dp[i][0] = dp[i - 1][0] + n / (double)i;
  }
  for (int i = 1; i <= n; i++)
    for (int j = 1; j <= n; j++) {
      dp[i][j] = ((n - j) * i * dp[i - 1][j] + (n - i) * j * dp[i][j - 1] +
                  i * j * dp[i - 1][j - 1] + n * n) /
                 ((n - j) * i + (n - i) * j + i * j);
    }
  printf("%lf\n", dp[n - l.size()][n - r.size()]);
  return 0;
}
