#include <cstring>
#include <algorithm>
#include <cstdio>
#include <iostream>
#define REP(i,a,b) for(i=a;i<b;i++)
#define rep(i,n) REP(i,0,n)

using namespace std;

typedef long long ll;
typedef unsigned long long ull;
typedef long double ld;
/* ここからが本編 */
/* */
int main(void)
{
  int i;
  ull n;
  ull a;
  cin >> n;
  a = n/2;
  printf("%llu\n",(a+1)*(n-a+1)-1);
  return 0;
}