#include<iostream>

 #include<cstring>

 #include<cstdio>

 #define M 100005

 #define ld long double

 int head[M],next[*M],u[*M],l[*M],n,m,cnt,du[M],v[M],root,now,fa[M],c[M];

 ld d[M],f[M],g[M],gg[M];

 using namespace std;

 void jia(int a1,int a2,int a3)

 {

     cnt++;

     u[cnt]=a2;

     l[cnt]=a3;

     next[cnt]=head[a1];

     head[a1]=cnt;

     return;

 }

 void dfs1(int a1)

 {

     v[a1]=;

     for(int i=head[a1];i;i=next[i])

       if(!v[u[i]]&&!c[u[i]])

         {

             dfs1(u[i]);

             du[a1]++;

             d[a1]+=f[u[i]]+(ld)l[i];

         }

     if(du[a1])

       f[a1]=d[a1]/(ld)du[a1];

     if(a1!=root)

       du[a1]++;

     return;

 }

 void dfs2(int a1)

 {

     v[a1]=;

     for(int i=head[a1];i;i=next[i])

       if(!v[u[i]]&&!c[u[i]])

         {

             int k=du[a1]-;

             if(!k)

               k++;

             d[u[i]]+=(d[a1]-f[u[i]]-(ld)l[i])/(ld)k+(ld)l[i];

             dfs2(u[i]);

         }

     return;

 }

 void zhao(int a1)

 {

     v[a1]=++now;

     for(int i=head[a1];i;i=next[i])

       if(!v[u[i]])

         {

             fa[u[i]]=a1;

             zhao(u[i]);

         }

       else  if(u[i]!=fa[a1]&&v[a1]>v[u[i]])

                {

                   c[u[i]]=;

                   for(;a1!=u[i];)

                     {

                         c[a1]=;

                         a1=fa[a1];

                     }

                }

     return;

 }

 void huan(int a1,int fa)

 {

     bool kg=;

     g[a1]=0.00000;

     for(int i=head[a1];i;i=next[i])

       if(c[u[i]]&&u[i]!=fa&&u[i]!=root)

          {

             kg=;

             huan(u[i],a1);

             g[a1]+=g[u[i]]+(ld)l[i];

          }

     if(a1==root)

       return;

     int k=du[a1];

     if(!k)

       k++;

     if(kg)

       g[a1]=d[a1]/(ld)k;

     else

       {

         k=du[a1]+;

         g[a1]=(g[a1]+d[a1])/(ld)k;

       }

 }

 int main()

 {

     scanf("%d%d",&n,&m);

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

       {

         int a1,a2,a3;

         scanf("%d%d%d",&a1,&a2,&a3);

         jia(a1,a2,a3);

         jia(a2,a1,a3);

       }

     if(n==m+)

       {

         root=;

         dfs1();

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

           v[i]=;

         dfs2();

       }

     else

       {

         zhao();

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

           v[i]=;

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

           if(c[i])

             {

                 root=i;

                 dfs1(i);

             }

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

           if(c[i])

             {

                 root=i;

                 huan(i,);

                 gg[i]=g[i];

             }

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

           if(c[i])

             {

                 du[i]+=;

                 d[i]+=gg[i];

             }

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

           v[i]=;

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

           if(c[i])

             dfs2(i);

       }

     double ans=0.00000;

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

       ans+=d[i]/(ld)du[i];

     printf("%.5lf\n",ans/(double)n);

     return ;

 }