bzoj1121:[POI2008]激光发射器SZK

传送门

读入输出题，看样例解释得出结论，具体原因不详
代码：

#include<cstdio>
#include<iostream>
#include<algorithm>
using namespace std;
void read(int &x) {
	char ch; bool ok;
	for(ok=0,ch=getchar(); !isdigit(ch); ch=getchar()) if(ch=='-') ok=1;
	for(x=0; isdigit(ch); x=x*10+ch-'0',ch=getchar()); if(ok) x=-x;
}
#define rg register
const int maxn=1e5+10;
int n;
int main()
{
	read(n);for(rg int i=1,x,y;i<=n;i++)read(x),read(y);
	printf("%d\n",n>>1);
}