#include <bits/stdc++.h>
using namespace std;
int main() {
  int count = 0, ndata, i;
  cin >> ndata;
  for (; i != 1;) {
    ndata = ndata - 2;
    count++;
    if (ndata == 0 || ndata - 1 == 0) {
      i = 1;
      if (ndata - 1 == 0) {
        count++;
      }
    }
  }
  cout << count;
  return 0;
}
