#include <bits/stdc++.h>
using namespace std;
int ans, x, dp[200];
int main() {
  cin >> x;
  dp[0] = 0;
  dp[1] = 1;
  for (int i = 2; i <= x; i++) {
    dp[i] = dp[i - 2] + i;
  }
  cout << dp[x];
}
