Sum

描述：

Consider the natural numbers from 1 to N. By associating to each number a sign (+ or -) and calculating the value of this expression we obtain a sum S. The problem is to determine for a given sum S the minimum number N for which we can obtain S by associating signs for all numbers between 1 to N.

For a given S, find out the minimum value N in order to obtain S according to the conditions of the problem.

输入：

The only line contains in the first line a positive integer S (0< S <= 100000) which represents the sum to be obtained.

输出：

The output will contain the minimum number N for which the sum S can be obtained.

输入样例：

12

0

输出样例：

7

3

解题思路：先对1~N求和，求出最大的范围，然后每当减一个数就是要减掉两倍的，就是减去偶数，所以只要Sum-sum是偶数即可。

代码如下：

#include<iostream>
usingnamespacestd;
intmain()
{
intstate=0;
intn;
cin>>n;
for(inti=1;;i++)
{
ints=i*(i+1)/2;
if(s<n)
continue;
if((s-n)%2==0)
{
cout<<i<<endl;
break;
}
}
return0;
}