#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ull = unsigned long long;
const ll INF = (int)1e17;
int main() {
  cin.tie(nullptr);
  std::ios_base::sync_with_stdio(false);
  cout.setf(std::ios_base::fixed);
  cout.precision(20);
  int n;
  cin >> n;
  vector<int> dp(n + 1);
  dp[1] = 1;
  dp[2] = 2;
  for (int i = 3; i <= n; i++) {
    dp[i] = i + dp[i - 2];
  }
  cout << dp[n];
  return 0;
}
