a042: 平面圓形切割 FYI: https://yunlinsong.blogspot.com/2016/02/blog-post_12.html

a042.cpp

#include <iostream>

using namespace std;

int main()
{
    int n;

    while( cin >> n )
    {
        n = 2 + (n-1)*(2 + 2 * (n - 1))/2;
        cout << n << endl;
    }

    return 0;
}