A - Most Unstable Array

import java.util.*;
public class MyClass {
    public static void main(String args[]) {
    Scanner sc = new Scanner(System.in);
    int t = sc.nextInt();
    while(t-->0){
        int n = sc.nextInt();
        int m = sc.nextInt();
         if(n==1){
            
            System.out.println(0);
            
        }
       else if(n==2){
            
            System.out.println(m);
            
        }
        else{
            System.out.println(m*2);
        }
        
    }
    
    }
}