//1085422276
#include<iostream>
#include<cstdio>
#include<cstring>
#include<string>
#include<algorithm>
#include<queue>
#include<cmath>
#include<map>
#include<bitset>
#include<set>
#include<vector>
using namespace std ;
typedef long long ll;
#define mem(a) memset(a,0,sizeof(a))
#define meminf(a) memset(a,127,sizeof(a));
#define memfy(a) memset(a,-1,sizeof(a))
#define TS printf("111111\n");
#define FOR(i,a,b) for( int i=a;i<=b;i++)
#define FORJ(i,a,b) for(int i=a;i>=b;i--)
#define READ(a,b) scanf("%d%d",&a,&b)
#define mod 1000000007
#define maxn 100000+5
inline ll read()
{
    ll x=0,f=1;
    char ch=getchar();
    while(ch<‘0‘||ch>‘9‘)
    {
        if(ch==‘-‘)f=-1;
        ch=getchar();
    }
    while(ch>=‘0‘&&ch<=‘9‘)
    {
        x=x*10+ch-‘0‘;
        ch=getchar();
    }
    return x*f;
}
//****************************************
int n,m;
double dp[maxn];
int ne[maxn];
int main()
{

    while(READ(n,m)!=EOF)
    {  mem(dp);memfy(ne);
    int x,y;
        if(n==0&&m==0)break;
        FOR(i,1,m)
        {
            scanf("%d%d",&x,&y);
            ne[x]=y;
        }
        FORJ(i,n-1,0)
        {
            if(ne[i]!=-1)dp[i]=dp[ne[i]];
            else {
                FOR(l,1,6)dp[i]+=(dp[i+l]/6.0);
                dp[i]+=1.0;
            }
        }
        printf("%.4f\n",dp[0]);
    }
    return 0;
}