#include <bits/stdc++.h>
using namespace std;
long long dp[101];
int main() {
  dp[1] = 1;
  dp[2] = 2;
  for (int i = 3; i < 101; i++) dp[i] = dp[i - 2] + i;
  int n;
  cin >> n;
  cout << dp[n] << endl;
}
