#include <bits/stdc++.h>
using namespace std;
const long long MX = (1 << 20);
using namespace std;
int cnt[MX];
int done[900];
int main() {
  int n;
  cin >> n;
  int ans = 1;
  for (int j = 2; j <= n; j++) {
    memset(done, 0, sizeof(done));
    for (int i = 0; i + j <= n; i++) {
      if (done[i]) continue;
      ++ans;
      for (int k = i; k + j <= n; k += j) done[k] = 1;
    }
  }
  cout << ans << endl;
}
