Zmei Gorynich

题意翻译

$T$组测试数据 每组数据 : 一条恶龙有$x$个头， 你有$n$个技能，每个技能无限使用：每次砍掉$d_i$个头，长出$h_i$个头，（砍掉后头数小于等于0时不再生长）， 问：最少使用多少次技能可以杀死恶龙，如果无法杀死，输出"-1"

题目描述

You are fighting with Zmei Gorynich — a ferocious monster from Slavic myths, a huge dragon-like reptile with multiple heads! Initially Zmei Gorynich has $ x $ heads. You can deal $ n $ types of blows. If you deal a blow of the $ i $ -th type, you decrease the number of Gorynich's heads by $ min(d_i, curX) $ , there $ curX $ is the current number of heads. But if after this blow Zmei Gorynich has at least one head, he grows $ h_i $ new heads. If $ curX = 0 $ then Gorynich is defeated. You can deal each blow any number of times, in any order. For example, if $ curX = 10 $ , $ d = 7 $ , $ h = 10 $ then the number of heads changes to $ 13 $ (you cut $ 7 $ heads off, but then Zmei grows $ 10 $ new ones), but if $ curX = 10 $ , $ d = 11 $ , $ h = 100 $ then number of heads changes to $ 0 $ and Zmei Gorynich is considered defeated. Calculate the minimum number of blows to defeat Zmei Gorynich! You have to answer $ t $ independent queries.

输入输出格式

输入格式

The first line contains one integer $ t $ ( $ 1 \le t \le 100 $ ) – the number of queries. The first line of each query contains two integers $ n $ and $ x $ ( $ 1 \le n \le 100 $ , $ 1 \le x \le 10^9 $ ) — the number of possible types of blows and the number of heads Zmei initially has, respectively. The following $ n $ lines of each query contain the descriptions of types of blows you can deal. The $ i $ -th line contains two integers $ d_i $ and $ h_i $ ( $ 1 \le d_i, h_i \le 10^9 $ ) — the description of the $ i $ -th blow.

输出格式

For each query print the minimum number of blows you have to deal to defeat Zmei Gorynich. If Zmei Gorynuch cannot be defeated print $ -1 $ .

输入输出样例

输入样例 #1

3
3 10
6 3
8 2
1 4
4 10
4 1
3 2
2 6
1 100
2 15
10 11
14 100

输出样例 #1

2
3
-1

说明

In the first query you can deal the first blow (after that the number of heads changes to $ 10 - 6 + 3 = 7 $ ), and then deal the second blow. In the second query you just deal the first blow three times, and Zmei is defeated. In third query you can not defeat Zmei Gorynich. Maybe it's better to convince it to stop fighting?