#include <bits/stdc++.h>

int main() {

  const int max = 2000000000;
  int A, B;
  std::cin >> A >> B;
  if( A < B ) {
    std::cout << B - 2 << std::endl;
  }
  else {
    std::cout << max - B - 1 << std::endl;
  }
  
  return 0;
}