public class ReduceToOneDigit
{
	public static void main(String[] args)
	{
		long x=123456789;					// call the method several times to demonstrate using different length long values
		System.out.println("Reducing " + x  + " to one digit gives us " + reduce(x));
		x=357;
		System.out.println("Reducing " + x  + " to one digit gives us " + reduce(x));		
		x=9999;
		System.out.println("Reducing " + x  + " to one digit gives us " + reduce(x));
		x=3525154;
		System.out.println("Reducing " + x  + " to one digit gives us " + reduce(x));
		x=9876985498999911l;
		System.out.println("Reducing " + x  + " to one digit gives us " + reduce(x));		
	}
	
	public static long reduce(long x)		
	{
		if(x<=9) return x;				// if x is a single digit (<=9) return it
		else return reduce(x%10+x/10);	// otherwise return the result of calling reduce by adding the rightmost digit (x%10) and the
				// rest of the number (x/10) 
	}
	
	// example:  x=12345, reduce(12345) = reduce(1+2345) = reduce (1 + 2 + 345) = reduce (1 + 2 + 3 + 45) = reduce (1 + 2 + 3 + 4 + 5)
	//			= reduce (15) = reduce (1 + 5) = reduce(6) = 6
}