public class Schachbrett {

  public static void main(String[] args) {

    // SANITY CHECKS

    if (args.length != 1) {
      System.out.println("Usage: java Schachbrett {number}");
      return;
    }

    int size;

    try {
      size = Integer.parseInt(args[0]);
    } catch (NumberFormatException nfe) {
      System.out.println("Please enter a valid number");
      return;
    }

    if (size <= 0) {
      System.out.println("Please enter a number above 0");
      return;
    }


    // DRAWING
    boolean isBlack = true;
    for(int x = 0; x < size; x++) {
      for(int y = 0; y < size; y++) {
        System.out.print(isBlack ? "*" : " ");
        isBlack = !isBlack;
      }
      System.out.print("\n");
    }
  }


}