#include <bits/stdc++.h>

using namespace std;

/*
 * Complete the pageCount function below.
 */
int pageCount(int n, int p) {
    /*
     * Write your code here.
     */
    long long minPage = min(p, n-p); //determine if page is closer to the end or the beginning.
    if(p == n-1 && n % 2 == 0)
    {
        return (minPage + 1) / 2;
    }
    //odd numbers are always on the right and evens are left.
    return minPage /2;

}

int main()
{
    ofstream fout(getenv("OUTPUT_PATH"));

    int n;
    cin >> n;
    cin.ignore(numeric_limits<streamsize>::max(), '\n');

    int p;
    cin >> p;
    cin.ignore(numeric_limits<streamsize>::max(), '\n');

    int result = pageCount(n, p);

    fout << result << "\n";

    fout.close();

    return 0;
}