#include <bits/stdc++.h>
using namespace std;
template <typename T>
void read(T &x)
{
	T sgn = 1;
	char ch = getchar();
	for (; !isdigit(ch); ch = getchar()) if (ch == '-') sgn = -1;
	for (x = 0; isdigit(ch); ch = getchar()) x = x * 10 + ch - '0';
	x *= sgn;
}
int n, m, g[10][10], deg[1 << 10];
double C[46][46];
double f[50][1 << 10];
int main()
{
	read(n); read(m);
	for (int i = 1, a, b; i <= m; i++)
	{
		read(a); read(b); a--; b--;
		g[a][b] = g[b][a] = 1;
	}
	for (int s = 0; s < (1 << n); s++)
		for (int i = 0; i < n; i++) if ((s >> i) & 1)
			for (int j = i + 1; j < n; j++) if ((s >> j) & 1)
				deg[s] += g[i][j];
	C[0][0] = 1;
	for (int i = 1; i <= m; i++)
	{
		C[i][0] = C[i][i] = 1;
		for (int j = 1; j < i; j++)
			C[i][j] = C[i - 1][j] + C[i - 1][j - 1];
	}
	for (int i = 0; i <= m; i++)
	{
		for (int s = 1; s < (1 << n); s++)
		{
			int id = __builtin_ctz(s);
			for (int t = s & (s - 1); t; t = s & (t - 1)) if ((t >> id) & 1)
			{
				for (int j = 0; j <= i; j++)
				{
					f[i][s] += C[deg[s ^ t]][i - j] * (C[deg[t]][j] - f[j][t]);
				}
			}
		}
	}
	double ans = 0;
	for (int i = 0; i <= m; i++)
	{
		ans += f[i][(1 << n) - 1] / C[deg[(1 << n) - 1]][i];
	}
	printf("%.6lf\n", ans / (m + 1));
	return 0;
}