3607：Traversal

Xiao Ming is travelling, and today he came to the West Lake, to see people playing a game, this game is like this, lake placed n-box, from 1 to n label. These boxes are floating in the water, there are some gold inside each box. Then participants from coast to jump the other side, each box have its’s height, you can only jump from lower height to higher height, and from a small label to a big label, you can skip some of the middle of the box. Suppose the minimum height is this side, the other side has the maximum height. Xiao Ming would like to jump how to get the most gold? He now needs your help.

There are multiple test cases. Each test case contains one integer N , representing the number of boxes . The following N lines each line contains two integers hi and gi , indicate the height and the number of gold of the ith box.
1 < = N < 100 001
0 < hi < 100 000 001
0 < gi < = 10000

For each test case you should output a single line, containing the number of maximum gold XiaoMing can get.