C++ :

#include<stdio.h>
struct node
{
	int  x, y;
}a[700];
int main()
{
	int n;
	while(scanf("%d",&n)!=EOF)
	{
		int max=0;int ax,ay;
		for (int i=0;i<n;i++)
			scanf("%d%d",&a[i].x,&a[i].y);
		for (int i=0;i<n-2;i++)
		{
			for (int j=i+1;j<n-1;j++)
			{
				int sum=0;
				for (int k=j+1;k<n;k++)
				{
					if (k!=i&&k!=j&&i!=j)
					{
						int as;
						as=a[i].x*a[j].y+a[j].x*a[k].y+a[k].x*a[i].y-a[k].x*a[j].y-a[k].y*a[i].x-a[j].x*a[i].y;
						if (as==0)  //用面积为0来证明三点共线
							sum++;
					}
				}
				if (max<sum) max=sum;
			}
		}
		printf("%d\n",max+2);
	}
}