#include <cstdio>

#include <cstring>

#include <iostream>

#include <cmath>

#include <algorithm>

#include <queue>

#include <vector>

using namespace std;

const int maxe = ;

const int maxn = ;

const int INF  = 0x3f3f3f;

double dp[maxn];

int map[maxn];

int main()

{

    //freopen("E:\\acm\\input.txt","r",stdin);

    int N,M;

    while(cin>>N>>M && N+M){

        for(int i=N;i<=N+;i++) dp[i] = ;

        memset(map,,sizeof(map));

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

            int x,y;

            scanf("%d %d",&x,&y);

            map[x] = y;

        }

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

            if(map[i]){

                dp[i] = dp[map[i]];

                continue;

            }

            int a[];

            double sum = ;

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

                a[j] = i+j;

                while(map[a[j]]){

                    a[j] = map[a[j]];

                }

                sum += dp[a[j]] + ;

            }

            dp[i] = sum/;

        }

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

    }

}