#include<cstdio>
#include<algorithm>
using namespace std;
const int N=100011;
const double eps=1e-8;
template<typename TP>void read(TP &kk){#define ak *TP phy=0,ioi=1;char ch=getchar();while(ch<'0'||ch>'9'){if(ch=='-')ioi=-1;ch=getchar();}while(ch>='0'&&ch<='9'){phy=phy*10+ch-'0';ch=getchar();}kk=phy ak ioi;
}
int n,m;
struct sumireko
{int to,ne,w;
}e[N*2];
int he[N],ecnt;
void addline(int f,int t,int w)
{e[++ecnt].to=t;e[ecnt].ne=he[f];he[f]=ecnt;e[ecnt].w=w;
}
bool onr[N];
double deg[N],sc[N],dpu[N],dpd[N];
void dfs1(int x,int f)
{for(int i=he[x],t;i;i=e[i].ne){t=e[i].to;if(t==f||onr[t]) continue;dfs1(t,x);dpd[x]+=dpd[t]+e[i].w;}if(sc[x]>eps) dpd[x]/=sc[x];
}
void dfs2(int x,int f)
{for(int i=he[x],t;i;i=e[i].ne){t=e[i].to;if(f==t||onr[t]) continue;dpu[t]=e[i].w;if(deg[x]-1.0>eps)dpu[t]+=(dpd[x]*sc[x]-e[i].w-dpd[t]+dpu[x]*(deg[x]-sc[x]))/(deg[x]-1.0);dfs2(t,x);}
}
int rnd[N],hp;
int sp;bool vv[N];
int find(int x,int f)
{if(vv[x]){sp=x;return 1;}vv[x]=1;int tmp;for(int i=he[x],t;i;i=e[i].ne){t=e[i].to;if(t==f) continue;if(tmp=find(t,x)){if(tmp==1){rnd[++hp]=x;onr[x]=1;if(x!=sp) return 1;}return 2;}}return 0;
}
double dpt[N];
void dfs3(int x,int f,int o,int s)
{if(!o){int g=0;for(int i=he[x],t;i;i=e[i].ne){t=e[i].to;if(!onr[t]) continue;g++;dfs3(t,x,g,s);dpu[x]+=dpt[t]+e[i].w;}dpu[x]/=2;return;}double tmp=0;dpt[x]=0;for(int i=he[x],t;i;i=e[i].ne){t=e[i].to;if(!onr[t]||t==s||t==f) continue;dfs3(t,x,o,s);dpt[x]+=dpt[t]+e[i].w;tmp+=1;}if(sc[x]+tmp>eps)dpt[x]=(dpt[x]+dpd[x]*sc[x])/(sc[x]+tmp);
}double ans;
int xi,yi,wi;
int main()
{read(n),read(m);for(int i=1;i<=m;i++){read(xi),read(yi),read(wi);addline(xi,yi,wi),addline(yi,xi,wi),deg[xi]+=1,deg[yi]+=1;}if(m==n-1){for(int i=1;i<=n;i++) sc[i]=deg[i]-1;sc[1]+=1;dfs1(1,0);dfs2(1,0);for(int i=1;i<=n;i++) ans+=(dpd[i]*sc[i]+dpu[i])/deg[i];ans/=n;printf("%.5lf\n",ans);return 0;}find(1,0);for(int i=1;i<=n;i++) sc[i]=deg[i]-(onr[i]?2.0:1.0);for(int i=1;i<=hp;i++) dfs1(rnd[i],0);for(int i=1;i<=hp;i++) dfs3(rnd[i],0,0,rnd[i]);for(int i=1;i<=hp;i++) dfs2(rnd[i],0);for(int i=1;i<=n;i++) ans+=(dpd[i]*sc[i]+dpu[i]*(deg[i]-sc[i]))/deg[i];ans/=n;printf("%.5lf\n",ans);return 0;
}