EXPEDI - Expedition

Xavier养的一群奶牛劫持了一个卡车，并向丛林中逃亡。由于奶牛们不会开车，卡车不幸地撞上了丛林中的一块岩石，并撞破了油箱。于是他们每行驶一个单位距离，油箱就漏一单位油。 为了修理这个卡车，奶牛们需要沿着一条长长的公路行驶到最近的一个城镇。在这条路上，在卡车当前位置和城镇之间，有N个加油站，每个加油站有不多于100单位的汽油。 丛林对于人类来说是个危险的地方，更不用说奶牛了。因此，奶牛们想要他们停下加油的次数尽量少。幸运的是，卡车的油箱是如此的大，可以容纳任意多的汽油。卡车现在距离城镇L单位长度，油箱里有P单位的油。 请求出奶牛们最少的加油次数，或者他们根本无法到达城镇，无解请输出-1 题目有多组数据 每组第一行有一个整数N(N <= 10 , 000)。 下面N行，每行两个整数，分别代表每个加油站与城镇的距离和本加油站拥有的汽油量。 每组最后一行有两个整数，L和P。(1 <= P <= 1 , 000 , 000) 如果奶牛们能到达城镇，输出一个整数，代表最少加油的次数。否则输出-1。

A group of cows grabbed a truck and ventured on an expedition deep into the jungle. Being rather poor drivers, the cows unfortunately managed to run over a rock and puncture the truck's fuel tank. The truck now leaks one unit of fuel every unit of distance it travels. To repair the truck, the cows need to drive to the nearest town (no more than 1,000,000 units distant) down a long, winding road. On this road, between the town and the current location of the truck, there are N (1 <= N <= 10,000) fuel stops where the cows can stop to acquire additional fuel (1..100 units at each stop). The jungle is a dangerous place for humans and is especially dangerous for cows. Therefore, the cows want to make the minimum possible number of stops for fuel on the way to the town. Fortunately, the capacity of the fuel tank on their truck is so large that there is effectively no limit to the amount of fuel it can hold. The truck is currently L units away from the town and has P units of fuel (1 <= P <= 1,000,000). Determine the minimum number of stops needed to reach the town, or if the cows cannot reach the town at all.

The first line of the input contains an integer t representing the number of test cases. Then t test cases follow. Each test case has the follwing form: - Line 1: A single integer, N - Lines 2..N+1: Each line contains two space-separated integers describing a fuel stop: The first integer is the distance from the town to the stop; the second is the amount of fuel available at that stop. - Line N+2: Two space-separated integers, L and P

For each test case, output a single integer giving the minimum number of fuel stops necessary to reach the town. If it is not possible to reach the town, output -1.

1
4
4 4
5 2
11 5
15 10
25 10

2

Input details The truck is 25 units away from the town; the truck has 10 units of fuel. Along the road, there are 4 fuel stops at distances 4, 5, 11, and 15 from the town (so these are initially at distances 21, 20, 14, and 10 from the truck). These fuel stops can supply up to 4, 2, 5, and 10 units of fuel, respectively. Output details: Drive 10 units, stop to acquire 10 more units of fuel, drive 4 more units, stop to acquire 5 more units of fuel, then drive to the town.