Farmer John has N cows that need to be milked (1 <= N <= 10,000), each of which takes only one unit of time to milk.</p>

Being impatient animals, some cows will refuse to be milked if Farmer John waits too long to milk them. More specifically, cow i produces g_i gallons of milk (1 <= g_i <= 1000), but only if she is milked before a deadline at time d_i (1 <= d_i <= 10,000). Time starts at t=0, so at most x total cows can be milked prior to a deadline at time t=x.

Please help Farmer John determine the maximum amount of milk that he can obtain if he milks the cows optimally.

입력 형식

• Line 1: The value of N.
• Lines 2..1+N: Line i+1 contains the integers g_i and d_i.

출력 형식

• Line 1: The maximum number of gallons of milk Farmer John can obtain.

예제 입력

4
10 3
7 5
8 1
2 1

예제 출력

25

힌트

Input Details

There are 4 cows. The first produces 10 gallons of milk if milked by time 3, and so on.

Output Details

Farmer John milks cow 3 first, giving up on cow 4 since she cannot be milked by her deadline due to the conflict with cow 3. Farmer John then milks cows 1 and 2.