Problem Description

You have N energy stones, each with initial energy and decay rate per second. You can collect one stone per second, and stones lose energy over time. Find the maximum total energy you can collect by choosing the optimal order.

Input Format

First line contains n (number of stones). Next n lines contain two integers: initial energy and decay rate per second.

Output Format

Maximum total energy that can be collected.

Constraints

• 1 ≤ n ≤ 1000

• 1 ≤ initial energy ≤ 1000

• 1 ≤ decay rate ≤ 100

• Stones with energy ≤ 0 cannot be collected

• Optimal ordering is crucial

Sample Input/Output

3
100 10
200 20
50 5

330

Explanation

Optimal order: collect stone 2 (200-20×0=200), then stone 1 (100-10×1=90), then stone 3 (50-5×2=40). Total: 200+90+40=330.