// This program counts the occurrences of the last digit of the triangle
// numbers.  The nth triangle number is equal to the sum of the first n
// integers (1 + 2 + 3 + ... + n) and is also equal to n * (n + 1) / 2.

public class TriangleCount {
	public static void main(String[] args) {
		int[] count = new int[100];
		for (int i = 1; i <= 10000; i++) {
			int next = i * (i + 1) / 2;
			int digits = next % 100;
			count[digits]++;
			if (i % 200 == 0) {
				System.out.print(".");
			}
		}
		System.out.println();
		for (int i = 0; i < count.length; i++) {
			if (count[i] != 0) {
				System.out.println("count for " + i + " = " + count[i]);
			}
		}
	}
}