#include<iostream>
using namespace std;

int main ()
{
    int n,k;
    cin >> n >> k;
    
    if (k==0 || n<k) { cout << 0 << endl; }
    else if(n-k+1 == n-(n-k)) {
        cout << n-1 << endl;
    }
    else {
        cout << n-2 << endl;
    }
    
    return 0;
    
}