#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, a;
  cin >> n >> a;
  if (a & 1) {
    cout << (a / 2 + 1) << endl;
  } else {
    cout << (1 + (n - a) / 2) << endl;
  }
  return 0;
}
