Cash Exchange

Time limit1sMemory limit256 MB

Summary
Given future daily prices of two vouchers and a fixed A-to-B buy ratio, find the most cash obtainable from S dollars after N days of buying and selling.
Level

Medium7 of 10

Topics
Dynamic programming, Math, Greedy, Implementation
Solved
No attempts yet

Problem

Little Y has recently been working at a currency exchange center. The currency exchange center only offers two types of vouchers to be exchanged: commemorative voucher A (henceforth known as voucher A) and commemorative voucher B (henceforth known as voucher B). All voucher-holding customers possess their very own account. The quantity of vouchers a customer has may be a real number.

Rising and falling daily with the waves of the market, the two types of vouchers each has their own values at any given time, and each unit of a voucher can be traded that day for some amount of cash. We note that on day K, the values of voucher A and voucher B are respectively AK and BK (dollars/unit voucher).

To make it more convenient for customers, the exchange center offers a very easy system to make transactions: the ratio exchange method. There are two different aspects to the ratio exchange method:

  1. Selling vouchers: the customer provides a real number OP in the range [0, 100] as the selling ratio. This means that OP% of voucher A and OP% of voucher B are exchanged for cash with the rate at that point in time.
  2. Buying vouchers: the customer pays IP dollars, and the exchange center takes this money to exchange it for vouchers. Furthermore, the ratio between the amount of voucher A and voucher B on day K just happens to be RateK.

For example, let's assume for the next 3 three days the following changes in the values of AK, BK, and RateK:

TimeAKBKRateK
Day 1111
Day 2122
Day 3223

Let's say that on one day, a customer has 100 dollars but no vouchers of any kind. The customer carry out the following transactions:

TimeTransactionCash (Dollars)Voucher AVoucher B
InitialNone10000
Day 1Buy - 100 dollars05050
Day 2Sell - 50%752525
Day 2Buy - 60 dollars155540
Day 3Sell - 100%20500

Note that there may be multiple transactions on a single day.

Little Y is a very economically-minded worker. After a relatively long time conducting operations and market estimates, he already knows within the future N days what the values of vouchers A and B, as well as rate will be. He wishes to calculate, if one starts with S dollars, what is the maximum amount of cash (in dollars) that can be obtained after N days.

Input

The first line contains two positive integers N and S, representing the number of days that little Y's can foresee and the starting amount of cash respectively.

Within the next N lines, the K-th line contains three real numbers AK, BK, and RateK.

Output

Output a single real number MaxProfit, indicating the maximum amount of cash in dollars that can be obtained after all operations on the N-th day has finished, accurate to 3 decimal places. Your answer will be considered correct if its absolute difference with the correct answer is no larger than 0.001.

Constraints

  • N ≤ 100 000
  • 0 < AK ≤ 10
  • 0 < BK ≤ 10
  • 0 < RateK ≤ 100
  • MaxProfit ≤ 109

Examples1

  1. Example 1

    Input
    3 100
    1 1 1
    1 2 2
    2 2 3
    
    Expected output
    225.000