#include <iostream>
#include <cmath>

using namespace std;

int main()
{
    int num;
    int sum = 0;

    cout << "计算 n+(n-1)+(n-2)+……+3+2+1= 的结果" << endl;
    cout << "请输入正整数n" << endl;
    cin >> num;

    if (num > 0)
    {
        while(num > 0) //循环求num~1的和
        {
        sum = sum + num;//循环相加
        num --;
        }
        cout << "输出的结果是" << sum << endl;
    }
   
    else
    {
        cout << "输入的数字有误，请重新输入" << endl;
    }


}