#include <iostream>#include <cstdio>#include <cstring>#include <algorithm>#define N 100005using namespace std;double p[N];struct e{	int u,v;	int next;}edge[1010];int head[N],tot;void addedge(int u,int v){	edge[tot].u=u;	edge[tot].v=v;	edge[tot].next=head[u];	head[u]=tot++;}int findx(int p){	int ret=p;	for(int ei=head[p];ei!=-1;ei=edge[ei].next){		ret=edge[ei].v;	}	return ret;}int main(){	int n,m,u,v,pos;	while(scanf("%d%d",&n,&m),n||m){		tot=0;		memset(head,-1,sizeof(head));		for(int i=1;i<=m;i++){			scanf("%d%d",&u,&v);			addedge(u,v);		}		p[n]=0;		for(int i=n-1;i>=0;i--){			p[i]=0;			if(head[i]!=-1){				p[i]=p[findx(i)];			}			else{				for(int k=1;k<=6;k++){					pos=i+k>n?n:i+k;					if(head[pos]!=-1){						p[i]+=p[findx(pos)]/6.0;					}					else{						p[i]+=p[pos]/6.0;					}				}				p[i]+=1;			}		}		printf("%.4lf\n",p[0]);	}	return 0;}