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No.1214 Market

レベル : / AI推定難易度 : 2200 / 実行時間制限 : 1ケース 2.000秒 / メモリ制限 : 512 MB / 標準ジャッジ問題
タグ : (AC するまで非表示) / 解いたユーザー数 11
作問者 : penguinman / テスター : kaage
お気に入りにしたユーザー ProblemId : 5034 / 自分の提出
問題文最終更新日: 2021-01-17 05:19:07
This statement was translated by AI (claude-opus-5-5, effort medium) and may contain errors or differ in nuance from the original. The original statement takes precedence. Back to the original
技術室奥プログラミングコンテスト#5 Day2 (順位表) の他の問題:

Problem Statement

Penguinman runs a market.

For this market, the following $4$ things have been decided at this point.

  • $N$ customers will come.
  • $M$ items will be sold. Each item has a fixed price and value: the price of the $i$-th item is $A_i$ yen and its value is $B_i$. It is guaranteed that $B_i≠B_j$ if $i≠j$.
  • Every customer brings an amount of money of their choice (an integer) between $0$ yen and $K$ yen, inclusive, with equal probability.
  • A customer buys exactly $1$ item: the one with the highest value among those affordable with the money they brought. A purchased item disappears from the market at that moment. If there is nothing they can buy, the customer gives up on shopping and goes home. Under the constraints of this problem, the item to buy is uniquely determined.
After learning the amount of money each customer brings, Penguinman has the customers shop at the market $1$ person at a time, in any order he chooses, so that the sum of the values of the items bought by the customers is maximized.

Your job, as Penguinman's subordinate, is to find the expected value of the sum of the values of the items bought by the customers.

It is guaranteed that this expected value can be expressed as $P/Q$ using $2$ positive integers $P,Q$. Find and print the integer $R$ between $0$ and $10^9+6$, inclusive, such that $R×Q≡P(\bmod 10^9+7)$.

Input

$N\ M\ K$
$A_1\ B_1$
$A_2\ B_2$
$︙$
$A_M\ B_M$
  • $1≤N,M≤40$
  • $1≤K≤10^9$
  • $1≤A_i≤K$
  • $1≤B_i≤10^9$
  • $B_i≠B_j$ if $i≠j$
  • All input values are integers.

Output

Print a newline at the end.

Sample

Sample 1
Input
2 1 2
1 1
Output
888888896

The sum of the values of the purchased items is $0$ only when neither of the $2$ customers brings even $1$ yen; in all other cases, the sum is $1$.
Therefore, the expected value is $8/3^2=8/9$, so the value to print is the integer $R$ such that $R×9≡8(\bmod 10^9+7)$, and the answer is $888888896$.

Sample 2
Input
10 3 100
2 4
5 100
1 101
Output
974312872

Sample 3
Input
40 6 1000000
400 100
20 1
1030 11
593 103
194029 103948
20 9183
Output
621015348

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