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>
#include <fstream>
#include <vector>
#include <bitset>
#include <unordered_map>
#include <algorithm>
  
using namespace std;

/********** TEMPLATE STARTS HERE ***********/
  
#define IOS ios::sync_with_stdio(false), cin.tie(0);
#define all(v) v.begin(), v.end()
#define F first
#define S second
#define pb push_back
#define test int t; cin >> t; while(t--)
#define skip continue
#define stop break
#define sz(v) v.size()
#define endl '\n'
#define PI 3.1415926535897932384626433832795
#define EPS 1e-9
#define gcd __gcd 
#define FO(i, a) for(auto & i : a)
#define debug(a) cout << #a << ": " << a << endl
#define debug1(a, l, r) FR(i, l, r) cout << a[i] << " "; cout << endl
#define SET(a, b) memset(a, b, sizeof(a));
#define refresh fflush(stdout);
  
typedef long long ll;
typedef pair <int, int> pii;
typedef pair <ll, ll> pll;
typedef vector <int> vi;
typedef vector <long long> vl;
typedef vector <pii> vii;
typedef vector <pll> vll;
  
const int INF = 0x3f3f3f3f;
const int LINF = 0x3f3f3f3f3f3f3f3f;
  
template <typename T, typename U> inline void amin(T &x, U y) { if(y < x) x = y; }
template <typename T, typename U> inline void amax(T &x, U y) { if(x < y) x = y; }
 
/*********** TEMPLATE ENDS HERE *************/

main()
{
	IOS
	int n;
	cin >> n;
	int odd = n / 2;
	int even = n / 2 + n % 2;
	cout << odd * even;
}