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