#include <bits/stdc++.h>
const int N = 2e3 + 7;
int n, m, x_have, y_have;
bool have[2][N];
long double f[N][N];
int main() {
  scanf("%d %d", &n, &m);
  for (register int i = 1, x, y; i <= m; i++) {
    scanf("%d %d", &x, &y);
    if (!have[0][x]) x_have += have[0][x] = true;
    if (!have[1][y]) y_have += have[1][y] = true;
  }
  for (register int i = 1; i <= n; i++) {
    f[i][0] = f[i - 1][0] + (long double)n / i;
    f[0][i] = f[0][i - 1] + (long double)n / i;
  }
  for (register int i = 1; i <= n - x_have; i++)
    for (register int j = 1; j <= n - y_have; j++)
      f[i][j] = (n * n + i * j * f[i - 1][j - 1] + i * (n - j) * f[i - 1][j] +
                 j * (n - i) * f[i][j - 1]) /
                (n * n - (n - i) * (n - j));
  return !printf("%.10Lf", f[n - x_have][n - y_have]);
}
