#include<bits/stdc++.h>
inline void read(int&a)
{
    a=0;char c=getchar();
    while(c<'0'||c>'9')c=getchar();
    while(c>='0'&&c<='9')
    {
        a=(a<<1)+(a<<3)+c-'0';
        c=getchar();
    }
}
inline void write(int a)
{
    if(a<0){putchar('-');a=-a;}
    if(a>9)write(a/10);
    putchar(a%10+'0');
}
#define smaxn 200001
#define pmaxn 1001
int n,m,d=-1;
int point[pmaxn],on_chain[pmaxn],next[smaxn],to[smaxn],len[smaxn];
double p[smaxn];
double ans=0.0;
inline void add(int a,int b,int c,double e)
{
    next[++d]=point[a];
    to[d]=b;
    len[d]=c;
    point[a]=d;
    p[d]=e;
}
int prior[pmaxn],dis[pmaxn];
int que[500000],start,end;
bool in_que[pmaxn],exist[smaxn];
inline int spfa()
{
    start=0;end=-1;
    memset(in_que,false,sizeof(in_que));
    memset(dis,0x7f,sizeof(dis));
    dis[1]=0;in_que[1]=true;que[++end]=1;
    while(end>=start)
    {
        int p=que[start],side=point[p];
        while(side!=-1)
        {
            if(exist[side]&&dis[to[side]]>dis[p]+len[to[side]])
            {
                prior[to[side]]=side;
                dis[to[side]]=dis[p]+len[side];
                if(!in_que[to[side]])
                {
                    que[++end]=to[side];
                    in_que[to[side]]=true;
                }
            }
            side=next[side];
        }
        in_que[p]=false;
        ++start;
    }
    if(dis[n]<dis[0])return dis[n];
    else return 0;
}
int main()
{
    memset(in_que,false,sizeof(in_que));
    memset(point,-1,sizeof(point));
    read(n);read(m);
    int u,v,l;
    double pi;
    for(int i=1;i<=m;i++)
    {
        read(u);read(v);read(l);scanf("%lf",&pi);
        add(u,v,l,pi);add(v,u,l,pi);
    }
    memset(on_chain,-1,sizeof(on_chain));
    memset(exist,true,sizeof(exist));
    int k=spfa(),q=0;
    double del=0;
    for(int i=2;i<=n;i++){del+=p[prior[i]];on_chain[++q]=prior[i];}
    ans+=(double)(k)*(1-del);
    for(int i=1;i<=q;i++)
    {
        if(p[on_chain[i]]>0&&on_chain[i]>-1)
        {
            exist[on_chain[i]]=false;exist[on_chain[i]^1]=false;
            ans+=(double)(spfa())*p[on_chain[i]];
            exist[on_chain[i]]=true;exist[on_chain[i]^1]=true;
        }
    }
    printf("%.7lf",ans);
    return 0;
}