思路：
1.按照耳背值升序排列。
2.两个索引树；第一个用来存放比之前耳背值大的牛的数量；第二个存放比比之前耳背值大的牛的位置和；其实是为了凑公式 val*(nx-sum(leftx)+sum(rightx)-nx);解释：简单推算，比当前牛耳背值小的坐标左边有几头牛，并且坐标和是多少?比当前牛耳背值小的坐标右边有几头牛，并且坐标和是多少?
package IndexTree;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.Arrays;
import java.util.Comparator;
import java.util.StringTokenizer;

public class Poj1990Wxc {

	static StringTokenizer st;
	static int  N;
	static Cow[] cowArray;
	static long[] tree;
	static long[] sumTree;
	static long A;
	public static void main(String[] args) throws IOException {
		// TODO Auto-generated method stub
		
		BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
		
		st=new StringTokenizer(br.readLine());
		
		N=Integer.parseInt(st.nextToken());
		
		cowArray=new Cow[N];
		
		int maxX=0;
		
		for(int i=0;i<N;i++)
		{
			
			st=new StringTokenizer(br.readLine());
			
			int  tempValue =Integer.parseInt(st.nextToken());
				
			int tempIndex=Integer.parseInt(st.nextToken());
			
			maxX=Math.max(maxX, tempIndex);
			
			Cow tmpCow=new Cow(tempIndex,tempValue);
			
			cowArray[i]=tmpCow;
			
		}
		
		Arrays.sort(cowArray, new Comparator<Cow>() {

			@Override
			public int compare(Cow o1, Cow o2) {
				// TODO Auto-generated method stub
				return o1.val-o2.val;
			}
		});
		
		int L=1;
		
		while(L<maxX)
		{
			L=L+L;
		}
		
		tree=new long[2*L];
		
		sumTree=new long[2*L];
		
		
		for(int i=0;i<cowArray.length;i++)
		{
			long leftCnt=queryCnt(L,cowArray[i].index+L);
			
			long rightCnt=queryCnt(cowArray[i].index+L,2*L-1);
			
			long leftSum=querySum(L,cowArray[i].index+L);
			
			long rightSum=querySum(cowArray[i].index+L,2*L-1);
			
			A=A+cowArray[i].val*(leftCnt*cowArray[i].index-leftSum+rightSum-rightCnt*cowArray[i].index);
			
		
				
			update(cowArray[i].index+L,1);
			
			updateSum(cowArray[i].index+L,cowArray[i].index);
			
			
		}
		System.out.println(A);
	}
	static long queryCnt(int start,int end)
	{
		long rnt=0;
		
		while(start<=end)
		{
			
			if(start%2==1)
			{
				rnt=rnt+tree[start];
			}
			
			if(end%2==0)
			{
				rnt=rnt+tree[end];
			}
			
			start=(start+1)>>1;
		
			end=(end-1)>>1;
			
		}
		
		return rnt;
	}
	
	static long querySum(int start,int end)
	{
		long rnt=0;
		
		while(start<=end)
		{
			
			if(start%2==1)
			{
				rnt=rnt+sumTree[start];
			}
			
			if(end%2==0)
			{
				rnt=rnt+sumTree[end];
			}
			
			start=(start+1)>>1;
		
			end=(end-1)>>1;
			
		}
		
		return rnt;
	}
	
	
	static void update(int index,long val)
	{
		while(index>0)
		{
			tree[index]=tree[index]+1;
			
			index=index>>1;
		}
	}
	
	static void updateSum(int index,long val)
	{
		while(index>0)
		{
			sumTree[index]=sumTree[index]+val;
			
			index=index>>1;
		}
	}
	
static class Cow{
	int index;
	
	int val;

	public Cow(int index, int val) {
		super();
		this.index = index;
		this.val = val;
	}

}
	
}