/* 
 * PROJECT EULER PROBLEM 1
 * If we list all the natural numbers below 10 that are multiples of 3 or 5, we get 3, 5, 6 and 9.
 * The sum of these multiples is 23.
 * Find the sum of all the multiples of 3 or 5 below 1000.
 * ans: 233168
 */
 
public class Euler.Problem1
{
	private const int ceiling = 1000;
 
	public Problem1() {
	}
 
	private int sum_divisible_by(int factor) {
		int s = 0;
		s = (factor * (((ceiling - 1) / factor) * (((ceiling - 1) / factor) + 1) * 1/2));
		return(s);
	}
 
	private void collect_sum() {
		int v = 0;
		v = sum_divisible_by(3) + sum_divisible_by(5) - sum_divisible_by(15);
		stdout.printf("sum = %d\n".printf(v));
	}
 
	public static int main(string[] args) {
		Euler.Problem1 p = new Euler.Problem1();
			p.collect_sum();
		return(0);
	}
}