public class Buttons {
    public static void main(String[] args) {
        //convert parameter into int
        int N = 0;
        try {
            N = Integer.parseInt(args[0]);
        } catch(NumberFormatException ignore) {}
        //find L
        for(int i = 3; i < Math.sqrt(N); i++) {
          if(N%i == 0) {
            System.out.println(i-1);
        System.exit(1);
          }
    }
    System.out.println(N-1);
    }
}
P.S. On my computer it works perfectly

Numbers are read from stdin