#include <iostream>
#include <cstring>
#include <cstdio>
#include <vector>
using namespace std;
int n, m, uu, vv, dy[100005];
double dp[100015];
int main(){
while(scanf("%d %d", &n, &m)!=EOF){
if(!n && !m) break;
memset(dp, 0, sizeof(dp));
memset(dy, 0, sizeof(dy));
for(int i=1; i<=m; i++){
scanf("%d %d", &uu, &vv);
dy[uu] = vv;
}
for(int i=n-1;i>=0; i--){
if(!dy[i])
dp[i] = (dp[i+1] + dp[i+2] + dp[i+3] + dp[i+4] + dp[i+5] + dp[i+6]) / 6.0 + 1.0;
else
dp[i] = dp[dy[i]];
}
printf("%.4lf
", dp[0]);
}
return 0;
}