WA #4#5#8#9，代码如下：

#include<bits/stdc++.h>
using namespace std;
struct node{
	int x,y;
}c[705];
bool operator<(node a,node b)
{
    if(a.x>=b.x) return false;
    else return true;
}
int main()
{
	int n,i,maxn=-1,sum=2;
	scanf("%d",&n);
	for(i=1;i<=n;i++) cin>>c[i].x>>c[i].y;
	stable_sort(c+1,c+n+1);
	for(i=2;i<n;i++)
	{
		if(c[i].x-c[i-1].x==c[i+1].x-c[i].x&&c[i].y-c[i-1].y==c[i+1].y-c[i].y)sum++;
		else sum=2;
		if(maxn<sum)maxn=sum;
	}
	printf("%d",maxn);
	return 0;
}