A9722 | Vanya and Exams

Vanya wants to pass $n$ exams and get the academic scholarship. He will get the scholarship if the average grade mark for all the exams is at least $avg$ . The exam grade cannot exceed $r$ . Vanya has passed the exams and got grade $a_{i}$ for the $i$ -th exam. To increase the grade for the $i$ -th exam by 1 point, Vanya must write $b_{i}$ essays. He can raise the exam grade multiple times.

What is the minimum number of essays that Vanya needs to write to get scholarship?

The first line contains three integers n, r, avg (1 ≤ n ≤ 105, 1 ≤ r ≤ 109, 1 ≤ avg ≤ min(r, 106)) — the number of exams, the maximum grade and the required grade point average, respectively.

Each of the following n lines contains space-separated integers ai and bi (1 ≤ ai ≤ r, 1 ≤ bi ≤ 106).

In the first line print the minimum number of essays.