1 #include<cstdio>
 2 #include<cstring>
 3 
 4 using namespace std;
 5 
 6 const int MAXN=1e5+10;
 7 const int MAXM=1e3+10;
 8 const double base=1.0/6.0;
 9 
10 double dp[MAXN];
11 int jump[MAXN];
12 
13 double con(int x)
14 {
15     double res=0.0;
16     for(int i=x;i<=x+5;i++)
17         res+=dp[i];
18     return res;
19 }
20 
21 int main()
22 {
23     int n,m;
24     while(scanf("%d%d",&n,&m))
25     {
26         if(!n&&!m)
27             break;
28         memset(jump,0,sizeof(jump));
29         for(int i=0;i<m;i++)
30         {
31             int u,v;
32             scanf("%d%d",&u,&v);
33             jump[u]=v;
34         }
35         memset(dp,0,sizeof dp);
36         for(int i=n-1;i>=0;i--)
37         {
38             if(jump[i])
39                 dp[i]=dp[jump[i]];
40             else
41                 dp[i]=base*con(i+1)+1;
42         }
43         printf("%.4f\n",dp[0]);
44     }
45     return 0;
46 }