#include <bits/stdc++.h>

using namespace std;

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

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