With highways available, driving a car from Hangzhou to any other city is easy. But since the tank capacity of a car is limited, we have to find gas stations on the way from time to time. Different gas station may give different PRice. You are asked to carefully design the cheapest route to go.

Input Specification:

Each input file contains one test case. For each case, the first line contains 4 positive numbers: Cmax (<= 100), the maximum capacity of the tank; D (<=30000), the distance between Hangzhou and the destination city; Davg (<=20), the average distance per unit gas that the car can run; and N (<= 500), the total number of gas stations. Then N lines follow, each contains a pair of non-negative numbers: Pi, the unit gas price, and Di (<=D), the distance between this station and Hangzhou, for i=1,…N. All the numbers in a line are separated by a space.

Output Specification:

For each test case, print the cheapest price in a line, accurate up to 2 decimal places. It is assumed that the tank is empty at the beginning. If it is impossible to reach the destination, print “The maximum travel distance = X” where X is the maximum possible distance the car can run, accurate up to 2 decimal places.

Sample Input 1: 50 1300 12 8 6.00 1250 7.00 600 7.00 150 7.10 0 7.20 200 7.50 400 7.30 1000 6.85 300 Sample Output 1: 749.17 Sample Input 2: 50 1300 12 2 7.10 0 7.00 600 Sample Output 2: The maximum travel distance = 1200.00 注：該貪心算法思想：設(shè)滿箱油時(shí)，車輛最遠(yuǎn)行駛距離為maxd 按距離排序后，最初處于起點(diǎn)加油站記為now，在距離該站maxd范圍內(nèi)，找出第一個(gè)比該站油價(jià)更低的站k，到k站加油，若找不到比now站低的站，就找距離該站maxd范圍內(nèi)now站除外油價(jià)最低的站k，到該站加油，更新now為k