HDU-2156 score matrix

Description

We define the following matrix:
1/1 1/2 1/3
1/2 1/1 1/2
1/3 1/2 1/1 The
diagonal elements of the matrix are always 1/1, and the diagonal scores on both sides 'S denominator increases one by one.
Request the sum of this matrix.

Input

Each row is given an integer N (N <50000), indicating that the matrix is ​​N * N. When N is 0, the input ends.

Output

Output the answer, keeping 2 decimal places.

Sample Input

1
2
3
4
0

Sample Output

1.00
3.00
5.67
8.83

#include <iostream>
#include <stdio.h>

using namespace std;

int main()
{
    int n;
    double sum;
    while (~scanf("%d", &n) && n!=0){
        sum = 0;
        for (int i =2 ; i <= n; i++)
            sum += (n-i+1)*2.0/i;
        printf("%.2f\n", sum+n);
    }
    return 0;
}