#include<bits/stdc++.h>
#define FILE "read"
#define MAXN 510
#define eps 1e-6
using namespace std;
struct node{int x,y;}e[MAXN*MAXN];
int n,m,d[MAXN];
double ans,c[MAXN*MAXN],a[MAXN][MAXN];
bool cmp(double a,double b){return a>b;}
char buf[1<<15],*fs,*ft;
inline char getc(){return (fs==ft&&(ft=(fs=buf)+fread(buf,1,1<<15,stdin),fs==ft))?0:*fs++;}
inline int read(){
int x=0,f=1; char ch=getc();
while(!isdigit(ch)) {if(ch=='-') f=-1; ch=getc();}
while(isdigit(ch)) {x=x*10+ch-'0'; ch=getc();}
return x*f;
}
void init(){
n=read(); m=read();
for(int i=1;i<=m;++i){
e[i].x=read();e[i].y=read();
d[e[i].x]++; d[e[i].y]++;
}
for(int i=1;i<=m;++i){
a[e[i].x][e[i].y]+=1.0/d[e[i].y];
a[e[i].y][e[i].x]+=1.0/d[e[i].x];
}
for(int i=1;i<=n;++i) a[n][i]=0;
for(int i=1;i<=n;++i) a[i][i]=-1;
a[1][n+1]=-1;
}
bool gauss(){
int now=1;
for(int i=1,temp;i<=n;++i){
for(temp=now;temp<=n;++temp)if(fabs(a[temp][i])>eps)break;
if(temp>n) continue;
if(now!=temp) swap(a[temp],a[now]);
double t=a[now][i];
for(int j=i+1;j<=n+1;++j) a[now][j]/=t;
for(int j=1;j<=n;++j)if(j!=now){
double t=a[j][i];
for(int k=i+1;k<=n+1;++k) a[j][k]-=t*a[now][k];
}
++now;
}
for(int i=now;i<=n;++i) if(fabs(a[i][n+1])>eps) return 0;
return 1;
}
void solve(){
gauss();
for(int i=1;i<=m;++i) c[i]=a[e[i].x][n+1]/d[e[i].x]+a[e[i].y][n+1]/d[e[i].y];
sort(c+1,c+m+1,cmp);
for(int i=1;i<=m;++i) ans+=c[i]*i;
printf("%.3lf\n",ans);
}
int main(){
freopen(FILE".in","r",stdin);
freopen(FILE".out","w",stdout);
init(); solve();
return 0;
}