#include <bits/stdc++.h>
using namespace std;
double dp[2222][2222];
int main() {
  int n, m;
  scanf("%d %d", &n, &m);
  set<int> cols, rows;
  for (int i = 0; i < m; ++i) {
    int r, c;
    scanf("%d %d", &r, &c);
    cols.insert(c);
    rows.insert(r);
  }
  int R = n - ((int)(rows).size());
  int C = n - ((int)(cols).size());
  dp[0][0] = 0;
  for (int i = 0; i <= R; ++i)
    for (int j = 0; j <= C; ++j) {
      if (i == 0 && j == 0) continue;
      double pUnRow = (double)i / n;
      double pUnCol = (double)j / n;
      dp[i][j] = 1;
      if (i > 0) dp[i][j] += pUnRow * (1 - pUnCol) * dp[i - 1][j];
      if (j > 0) dp[i][j] += (1 - pUnRow) * pUnCol * dp[i][j - 1];
      if (i > 0 && j > 0) dp[i][j] += pUnRow * pUnCol * dp[i - 1][j - 1];
      dp[i][j] = dp[i][j] / (1 - (1 - pUnRow) * (1 - pUnCol));
    }
  printf("%.10lf\n", dp[R][C]);
  return 0;
}
