BEHAPPY  Be Awesome As Barney Stinson
Barney Stinson ;) is way too flirty. He has many girlfriends and he wants to keep all of them happy. He has M girlfriends. He bought N gifts for them. Now he knows that some girlfriends need more gifts and some need less. So he decided that he will give atleast Ai gifts and at most Bi gifts to his ith girlfriend. He has to give away all the N gifts. Tell us in how many different ways he can do this.
INPUT
For each test case, first line contains two integers M and N, then follows M lines each having two integers Ai and Bi (1 <= i <= M). Input ends with M and N both equal to 0 and that case should not be processed.
OUTPUT:
For each test case, output the number of different ways in which he can distribute those gifts in a single line.
Constraints
1 <= M <= 20, 1 <= N <= 100, 0 <= Ai, Bi <=100
Example
Input:
3 5 0 1 1 3 1 4 0 0
Output:
6
Explanation
He can distribute 5 gifts in his 3 girlfriends in 6 different ways as follows (0 1 4), (0 2 3), (0 3 2), (1 1 3), (1 2 2), (1 3 1).
hide comments
zakir068:
20190302 17:49:45
good problem for the newbies :) 

anshuman16423:
20180926 05:51:11
AC in one GO!!! simple DP and recusrsion


egoista_:
20180627 08:51:00
Straight forward dp. AC in one go. 

aman_sachin200:
20180615 10:33:53
Same problem UOFTAE!! :P 

luka_dzimba911:
20180323 18:23:54
Do not test this problem on spoj toolkit , it gives WA on corner cases


waqar_ahmad224:
20180318 06:19:06
so easy that i solved using only recursion (No dp ) in 1 go , with time 0.00 sec 

shahzada:
20170306 04:56:51
Should be moved to tutorial. 

kshubham02:
20170222 06:36:06
1. I realized after submitting that I am not even taking multiple test cases. Just inputting M and N once, no breaking at 0 0 or any of that shit.


.::Austin::.:
20160709 14:07:20
wth!!! exponential passes in 0.00s 

GAURAV CHANDEL:
20160428 11:25:24
Be Happy .. with DP .. 
Added by:  Ankit Kumar Vats 
Date:  20111021 
Time limit:  1s 
Source limit:  50000B 
Memory limit:  1536MB 
Cluster:  Cube (Intel G860) 
Languages:  All except: ASM64 
Resource:  Inspired 