#include <cstdio>
#include <vector>
#include <algorithm>
#include <cmath>
using namespace std;

typedef vector<double> V;
typedef vector<V> M;
#define eps 1e-8
#define N 12
int n,m;
vector<int> es[N];
double tbl[1<<N][N];

int gauss(M& a, V& b, V& x) 
{
  int m=a.size(),n=a[0].size(),k,r;
  vector<int> q;
  for (k=0;k<min(m,n);++k) {
    int i,j;
    for(j=k;j<n;j++)
      for(i=k;i<m;i++)
        if (abs(a[i][j])>eps) goto FOUND;
    break;
  FOUND:
    if (j!=k) for (int t=0;t<m;++t) swap(a[t][j], a[t][k]);
    q.push_back(j);
    if (i!=k) { swap(a[i],a[k]); swap(b[i],b[k]); }
    for (int j=k+1;j<m;++j)
      if (abs(a[j][k])>eps) {
        double l =a[j][k]/a[k][k];
        for (int i=k+1;i<n;++i) a[j][i]=a[j][i]-(l*a[k][i]);
        b[j] =b[j]-(l*b[k]);
      }
  }
  r=k;
  x.clear(); x.resize(n,0);
  for (int k=r;k<m;++k) if (abs(b[k])>eps) return -1;
  for (int k=r-1;k>=0;--k) {
    double s=b[k];
    for (int j=k+1;j<r;++j) s=s-(a[k][j]*x[j]);
    x[k]=s/a[k][k];
  }
  for (int k=r-1;k>=0;--k) swap(x[k], x[q[k]]);
  return n-r;
}


int main() {
	scanf("%d%d",&n,&m);
	for (int i=0;i<m;++i) {
		int a,b; scanf("%d%d",&a,&b); --a,--b;
		es[a].push_back(b);
		es[b].push_back(a);
	}
	for (int v=0;v<n;++v)	tbl[(1<<n)-1][v]=0;
	
	for (int seen=(1<<n)-2;seen>=0;--seen) {
		M A(n+1,V(n+1,0));
		V b(n+1,0);
		V x;

		for (int v=0;v<n;++v) {
			A[v][n]+=1;
			A[v][v]-=1;
			for (int i=0;i<es[v].size();++i) {
				int nv=es[v][i];
				if (seen&(1<<nv)) {
					A[v][nv]+=1.0/es[v].size();
				} else {
					A[v][n]+=tbl[seen|(1<<nv)][nv]/es[v].size();
				}
			}
		}
		A[n][n]=1;
		b[n]=1;
		gauss(A,b,x);
		for (int v=0;v<n;++v) tbl[seen][v]=x[v];
	}

	printf("%.6lf\n",tbl[1][0]);
}