1 #include <cstdio>
 2 #include <cstring>
 3 #include <algorithm>
 4 #include <vector>
 5 using namespace std;
 6 #define N 100010
 7 
 8 double dp[N];
 9 int nxt[N];
10 
11 int main()
12 {
13     int n, m;
14     while(~scanf("%d%d", &n, &m), n+m) {
15         memset(nxt, -1, sizeof(nxt));
16         for(int i = 0; i < m; i++) {
17             int u, v;
18             scanf("%d%d", &u, &v);
19             nxt[u] = v;
20         }
21         memset(dp, 0, sizeof(dp));
22         double dec = (double)1 / 6;
23         for(int i = n - 1; i >= 0; i--) {
24             if(nxt[i] != -1) {
25                 dp[i] = dp[nxt[i]]; //如果可以飞，就直接把上一步的值赋给它
26                 continue;
27             }
28             for(int j = 1; j <= 6; j++) {
29                 if(i + j <= n) {
30                     dp[i] += dp[i + j] * dec; //不能飞的话，就掷骰子为1-6的概率都为1/6，递推
31                 }
32             }
33             dp[i]++; //走到下一步要+1
34         }
35         printf("%.4f\n", dp[0]);
36     }
37     return 0;
38 }