Waht is the problem in this code?

import java.util.Scanner;

public class LastCheck {
public static void main(String args[]){
int a;
Scanner s= new Scanner(System.in);
a=s.nextInt();
String ar[]=new String[a];
System.out.println(ar.length);
for(int i=0;i<ar.length;++i)
{
    ar[i]=s.nextLine();

}

for(int i=0;i<ar.length;++i)
{
     String n1=ar[i].substring(0,ar[i].indexOf(" ")); 
   String n2=ar[i].substring(ar[i].indexOf(" ")+1);  
System.out.println(n1);    
System.out.println(n2);
}
}
}