Description：
Amr lives in Lala Land. Lala Land is a very beautiful country that is located on a coordinate line. Lala Land is famous with its apple trees growing everywhere.
Lala Land has exactly n apple trees. Tree number i is located in a position xiand has ai apples growing on it. Amr wants to collect apples from the apple trees. Amr currently stands in x = 0 position. At the beginning, he can choose whether to go right or left. He'll continue in his direction until he meets an apple tree he didn't visit before. He'll take all of its apples and then reverse his direction, continue walking in this direction until he meets another apple tree he didn't visit before and so on. In the other words, Amr reverses his direction when visiting each new apple tree. Amr will stop collecting apples when there are no more trees he didn't visit in the direction he is facing.
What is the maximum number of apples he can collect?
Input
The first line contains one number n (1 ≤ n ≤ 100), the number of apple trees in Lala Land.
The following n lines contains two integers each xi, ai ( - 105 ≤ xi ≤ 105, xi ≠ 0, 1 ≤ ai ≤ 105), representing the position of the i-th tree and number of apples on it.
It's guaranteed that there is at most one apple tree at each coordinate. It's guaranteed that no tree grows in point 0.
Output
Output the maximum number of apples Amr can collect.
Examples
Input
2 -1 5 1 5
Output
10
Input
3 -2 2 1 4 -1 3
Output
9
Input
3 1 9 3 5 7 10
Output
9
Note
In the first sample test it doesn't matter if Amr chose at first to go left or right. In both cases he'll get all the apples.
In the second sample test the optimal solution is to go left to x = - 1, collect apples from there, then the direction will be reversed, Amr has to go to x = 1, collect apples from there, then the direction will be reversed and Amr goes to the final tree x = - 2.
In the third sample test the optimal solution is to go right to x = 1, collect apples from there, then the direction will be reversed and Amr will not be able to collect anymore apples because there are no apple trees to his left.
题意：
给出n个苹果树，每行包括树的距离和他的苹果数量，每次可以选择向左或者向右走，每次遇到树就向相反方向走，求最多获得的苹果数量。
以0为中点，分为左右两个区间，树少的那一边肯定可以全部得到，多的那一边最多可以得到少的数的数量+1棵树，分为两个区间排序模拟就行
AC代码：
#include <bits/stdc++.h>
using namespace std;
struct tree
{
int x,p;
};
tree t1[110];
tree t2[110];
bool cmp(tree aa,tree bb)
{
return aa.x<bb.x;
}
int n,m;
int i,j,k,l,a,b;
int main()
{
while(~scanf("%d",&n))
{
int cnt1=0,cnt2=0;
for(i=0;i<n;i++)
{
scanf("%d %d",&a,&b);
if(a<0)
t1[cnt1].x=-a,t1[cnt1++].p=b;
else
t2[cnt2].x=a,t2[cnt2++].p=b;
}
sort(t1,t1+cnt1,cmp);
sort(t2,t2+cnt2,cmp);
int num;
num=min(cnt1,cnt2);
int ans=0;
for(i=0;i<num;i++)
ans+=(t1[i].p+t2[i].p);
if(cnt1>cnt2)
ans+=t1[cnt2].p;
if(cnt1<cnt2)
ans+=t2[cnt1].p;
printf("%d\n",ans);
}
return 0;
}
