Sum of Two Integers（规律题）

Time Limit: 2 sec / Memory Limit: 1024 MB

Score : 100 points

Problem Statement

How many ways are there to choose two distinct positive integers totaling N, disregarding the order?

Constraints

·1≤N≤1000000
·N is an integer.

Input

Input is given from Standard Input in the following format:

N

Output

Print the answer.

Sample Input 1

4

Sample Output 1

1
There is only one way to choose two distinct integers totaling 4: to choose 1 and 3. (Choosing 3 and 1 is not considered different from this.)

Sample Input 2

999999

Sample Output 2

499999

题意：给定一个N，用2个不相等的数字相加等于N即算一种（这两个数字交换位置算一种情况）。当N为奇数时，结果为N/2，当N为偶数时，结果为N/2-1。

#include<iostream>
#include<cstdio>
#include<cmath>
using namespace std
int main()
{
	int N
	scanf("%d", &N)
	if (N % 2 == 0)
		printf("%dn", N / 2 - 1)
	else
		printf("%dn", N / 2)
	return 0
}