1 #include<bits/stdc++.h>
 2 #define F(i,a,b) for(int i=a;i<=b;++i)
 3 using namespace std;
 4 
 5 const int N=1e5+7;
 6 double dp[N];
 7 int n,m,vis[N];
 8 
 9 int main(){
10     while(scanf("%d%d",&n,&m),n+m)
11     {
12         F(i,0,n)vis[i]=-1;
13         F(i,1,m)
14         {
15             int x,y;
16             scanf("%d%d",&x,&y);
17             vis[x]=y;
18         }
19         F(i,0,n+6)dp[i]=0;
20         for(int i=n-1;i>=0;i--)
21         {
22             if(vis[i]!=-1){dp[i]=dp[vis[i]];continue;}
23             F(j,1,6)dp[i]+=dp[i+j]/6;
24             dp[i]+=1;
25         }
26         printf("%.4f\n",dp[0]);
27     }
28     return 0;
29 }