Three product

Given a set of positive integers s = {a1, a2, ..., an},
There exists ai * aj = ak,  i != j != k
Find the maximum number satisfying the above conditions, if there are no three numbers satisfying the above condition, the output –1

public static int findProduct(int a[]) {
		int n = a.length;

		for (int i = 0; i < n; i++) {
			for (int j = 0, k = i + 1; j < i && k < n;) {
				if (a[i] * a[j] == a[k]) {
					return a[k]; // find
				} else if (a[i] * a[j] > a[k])
					k++;
				else
					j++;
			}
		}

		return -1;
	}