Problem:
Score : 100 points

Problem Statement

Find the number of ways to choose a pair of an even number and an odd number from the positive integers between 1 and K (inclusive). The order does not matter.

Constraints

2\leq K\leq 100

K is an integer.

Input

Input is given from Standard Input in the following format:

K

Output

Print the number of ways to choose a pair of an even number and an odd number from the positive integers between 1 and K (inclusive).

Sample Input 1

3

Sample Output 1

2

Two pairs can be chosen: (2,1) and (2,3).

Sample Input 2

6

Sample Output 2

9

Sample Input 3

11

Sample Output 3

30

Sample Input 4

50

Sample Output 4

625

Solution in C++14 (GCC 5.4.1) (judge verdict: Accepted)

#include <bits/stdc++.h>

#define rep(x, y) for (int i = (x); i < (y); i++)

typedef long long ll;

using namespace std;

int main() {
    int k;
    cin >> k;

    int cnt = 0;
    for (int i = 1; i <= k; i++) {
        for (int j = 1; j <= k; j++) {
            if (i % 2 == 0 && j % 2 != 0) cnt++;
        }
    }

    cout << cnt << endl;

    return 0;
}