Consider the following program fragment, which has a time complexity that is a function of n. What is its time complexity using Big-O notation>

int sum = 0;

for (int k = 1; k < n; k = 2*k) {

for (int m = 1; m < k; m = 2*m) {

sum = sum + m;

}

}

Please explain how you got your answer in detail because I'd like to understand this problem. Thank you!! :)