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