#include <bits/stdc++.h>

using namespace std;

#define REP(i,a,b) for(int i=a;i<(int)b;i++)
#define rep(i,n) REP(i,0,n)

int main() {
  
  long long n; cin >> n;
  long long mx = -1<<29;
  REP(K, 1, n) {
    long long N = n;
    N -= 2*K;
    N /= 2;
    mx = max(mx, K*N);
  }
  cout << mx << endl;
  
  return 0;
}