cho.shTime limit
2s
Memory limit
256 MB
Sangwook, a teaching assistant, gave Dongho N problems and announced how many cups of ramen Dongho would receive for solving each one. Because Dongho was extremely confident, Sangwook also assigned a deadline to each problem.
| Problem number | 1 | 2 | 3 | 4 | 5 | 6 | 7 |
|---|---|---|---|---|---|---|---|
| Deadline | 1 | 1 | 3 | 3 | 2 | 2 | 6 |
| Cups of ramen | 6 | 7 | 2 | 1 | 4 | 5 | 1 |
In the situation above, if Dongho solves the problems in the order 2, 6, 3, 1, 7, 5, 4, then problems 2, 6, 3, and 7 are completed before their deadlines. He receives a total of 15 cups of ramen.
Find the maximum number of cups of ramen Dongho can receive. In the situation above, the maximum is 15.
Solving one problem takes exactly 1 unit of time. Every deadline is a positive integer not greater than N. The number of cups awarded for each problem, and the maximum total number of cups Dongho can receive, are positive integers less than 2^31.
The first line contains the number of problems N (1 ≤ N ≤ 200,000).
Each of the next N lines contains two integers separated by a space: the deadline of the i-th problem and the number of cups of ramen received for solving it.
Print the maximum number of cups of ramen Dongho can receive.