#include <iostream>

using namespace std;

int main() {
    long long a, b;
    cin >> a >> b;
    if (a == 1 || b == 2000000000){
        cout << 0;
    }else if (a < b) {
        cout << a - 1;
    } else {
        cout << 2000000000 - b - 1;
    }
}