F.A.Q
Hand In Hand
Online Acmers
Problem Archive
Realtime Judge Status
Authors Ranklist

C/C++/Java Exams
ACM Steps
Go to Job
Contest LiveCast
ICPC@China
Best Coder beta
VIP | STD Contests
DIY | Web-DIY beta
Register new ID

# Aeroplane chess

Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 32768/32768 K (Java/Others)
Total Submission(s): 8346    Accepted Submission(s): 5183

Problem Description
Hzz loves aeroplane chess very much. The chess map contains N+1 grids labeled from 0 to N. Hzz starts at grid 0. For each step he throws a dice(a dice have six faces with equal probability to face up and the numbers on the faces are 1,2,3,4,5,6). When Hzz is at grid i and the dice number is x, he will moves to grid i+x. Hzz finishes the game when i+x is equal to or greater than N.

There are also M flight lines on the chess map. The i-th flight line can help Hzz fly from grid Xi to Yi (0<Xi<Yi<=N) without throwing the dice. If there is another flight line from Yi, Hzz can take the flight line continuously. It is granted that there is no two or more flight lines start from the same grid.

Input
There are multiple test cases.
Each test case contains several lines.
The first line contains two integers N(1¡ÜN¡Ü100000) and M(0¡ÜM¡Ü1000).
Then M lines follow, each line contains two integers Xi,Yi(1¡ÜXi<Yi¡ÜN).
The input end with N=0, M=0.

Output
For each test case in the input, you should output a line indicating the expected dice throwing times. Output should be rounded to 4 digits after decimal point.

Sample Input
2 0
8 3
2 4
4 5
7 8
0 0


Sample Output
1.1667
2.3441


Source

Statistic | Submit | Discuss | Note
 Home | Top Hangzhou Dianzi University Online Judge 3.0 Copyright © 2005-2024 HDU ACM Team. All Rights Reserved. Designer & Developer : Wang Rongtao LinLe GaoJie GanLu Total 0.000000(s) query 1, Server time : 2024-04-15 23:12:02, Gzip enabled Administration