#include<cstdio>

 #include<cstring>

 #include<algorithm>

 #include<cstdlib>

 #include<cmath>

 #include<iostream>

 using namespace std;

 typedef long long ll;

 //const int inf=0x3f3f3f3f;

 const int maxn=1e5+;

 int v[maxn];

 double dp[maxn];

 int main(){

     ios::sync_with_stdio();

     int n,m,a,b;

     while(cin>>n>>m&&(n||m)){

         memset(dp, , sizeof dp);

         memset(v, , sizeof v);

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

             cin>>a>>b;

             v[a]=b;

         }

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

             if(v[i]){

                 dp[i]=dp[v[i]];

                 continue;

             }

             for(int j=;j<=;j++){

                 dp[i]+=dp[i+j]/6.0;

             }

             dp[i]+=;

         }

         printf("%.4f\n",dp[]);

     }

 }