Building Shops

HDU’s $n$ classrooms are on a line ,which can be considered as a number line. Each classroom has a coordinate. Now Little Q wants to build several candy shops in these $n$ classrooms.

The total cost consists of two parts. Building a candy shop at classroom $i$ would have some cost $c_i$. For every classroom $P$ without any candy shop, then the distance between $P$ and the rightmost classroom with a candy shop on $P$'s left side would be included in the cost too. Obviously, if there is a classroom without any candy shop, there must be a candy shop on its left side.

Now Little Q wants to know how to build the candy shops with the minimal cost. Please write a program to help him.

The input contains several test cases, no more than 10 test cases.
In each test case, the first line contains an integer $n(1\leq n\leq 3000)$, denoting the number of the classrooms.
In the following $n$ lines, each line contains two integers $x_i,c_i(-10^9\leq x_i,c_i\leq 10^9)$, denoting the coordinate of the $i$-th classroom and the cost of building a candy shop in it.
There are no two classrooms having same coordinate.

For each test case, print a single line containing an integer, denoting the minimal cost.

3
1 2
2 3
3 4
4
1 7
3 1
5 10
6 1

5
11

2017中国大学生程序设计竞赛 - 女生专场