/**************************************************************

     Problem: 3143

     User: rausen

     Language: C++

     Result: Accepted

     Time:680 ms

     Memory:6792 kb

 ****************************************************************/

 #include <cstdio>

 #include <cmath>

 #include <algorithm>

 using namespace std;

 typedef double lf;

 const int N = ;

 const int M = N * N;

 const lf eps = 1e-;

 int read();

 int n, m, tot;

 int deg[N];

 lf a[N][N], ans[N], w[M];

 lf Ans;

 struct edge {

     int x, y;

 } E[M];

 inline void Add_Edges(int x, int y) {

     E[++tot].x = x, E[tot].y = y;

     a[x][y] = a[y][x] = -1.0;

     ++deg[x], ++deg[y];

 }

 void gauss(int n) {

     int i, j, k;

     lf tmp;

     for (i = ; i <= n; ++i) {

         for (k = i, j = i + ; j <= n; ++j)

             if (fabs(a[j][i]) > fabs(a[k][i])) k = j;

         if (fabs(a[k][i]) < eps) continue;

         for (j = i; j <= n + ; ++j) swap(a[i][j], a[k][j]);

         for (k = i + ; k <= n; ++k)

             for (tmp = -a[k][i] / a[i][i], j = i; j <= n + ; ++j)

                 a[k][j] += a[i][j] * tmp;

     }

     for (i = n; i; --i) {

         for (j = i + ; j <= n; ++j)

             a[i][n + ] -= a[i][j] * ans[j];

         ans[i] = a[i][n + ] / a[i][i];

     }

 }

 int main() {

     int i, j;

     n = read(), m = read();

     for (i = ; i <= m; ++i)

         Add_Edges(read(), read());

     for (i = ; i < n; ++i) {

         for (j = ; j < n; ++j)

             if (deg[j]) a[i][j] = a[i][j] / deg[j];

         a[i][i] = , a[i][n] = ;

     }

     a[][n] = ;

     gauss(n - );

     for (i = ; i <= n; ++i)

         if (deg[i]) ans[i] /= deg[i];

     for (i = ; i <= m; ++i)

         w[i] = ans[E[i].x] + ans[E[i].y];

     sort(w + , w + m + );

     for (i = ; i <= m; ++i) Ans += w[i] * (m - i + );

     printf("%.3lf\n", Ans);

     return ;

 }

 inline int read() {

     static int x;

     static char ch;

     x = , ch = getchar();

     while (ch < '' || '' < ch)

         ch = getchar();

     while ('' <= ch && ch <= '') {

         x = x *  + ch - '';

         ch = getchar();

     }

     return x;

 }