#include <bits/stdc++.h>
using namespace std;
const int N = 2005;
int n, m, r, l, x[N], y[N];
double dp[N][N];
void init() {
  memset(x, 0, sizeof(x));
  memset(y, 0, sizeof(y));
  scanf("%d%d", &n, &m);
  int a, b;
  r = l = n;
  for (int i = 0; i < m; i++) {
    scanf("%d%d", &a, &b);
    if (x[a] == 0) r--;
    if (y[b] == 0) l--;
    x[a]++;
    y[b]++;
  }
}
double solve() {
  dp[0][0] = 0;
  for (int i = 1; i <= n; i++) {
    dp[i][0] = dp[i - 1][0] + n * 1.0 / i;
    dp[0][i] = dp[0][i - 1] + n * 1.0 / i;
  }
  for (int i = 1; i <= r; i++) {
    for (int j = 1; j <= l; j++) {
      dp[i][j] = n * n;
      dp[i][j] += i * j * dp[i - 1][j - 1];
      dp[i][j] += i * (n - j) * dp[i - 1][j];
      dp[i][j] += (n - i) * j * dp[i][j - 1];
      dp[i][j] /= (n * n - (n - i) * (n - j));
    }
  }
  return dp[r][l];
}
int main() {
  init();
  printf("%.10lf\n", solve());
  return 0;
}
