#include <bits/stdc++.h>
using namespace std;
const int MAXN = 100;
int mem[MAXN + 10];
int main() {
  int N;
  cin >> N;
  mem[0] = 0, mem[1] = 1, mem[2] = 2, mem[3] = 4;
  for (int i = 4; i <= N; ++i) {
    mem[i] = i + mem[i - 2];
  }
  cout << mem[N] << '\n';
}
