Time complexity in s.java

public static void main(String[] args) {
	long startTime = System.currentTimeMillis();
	
	int n = 100 * 1000;
	long res = compute(n);
	
	long endTime = System.currentTimeMillis();
	System.out.println(res);
	
	// 2.2 GHz ~ 2.2 * 10^9 op/sec
	// alg ~ n^2 op ~ 10^10 op
	// total time: 10^10 / (22 * 10^8) ~ 4 sec
	
	// let's double the input:
	// n = 200000
	// totatl time = prev_time * 4 ~ 16 sec
	System.out.println((endTime - startTime) / 1000);
}
​
static long compute(int n) {
	long sum = 0;
	for (int i = 0; i < n; ++i) {
		for(int j = 0; j < n; ++j) {
			sum += i*j;
		}
	}
	return sum;
}