Consider the following description of an algorithm: Given a list of n integers and 3 target integers, a, b, and c: First, perform linear search for element a; if it is found, return its index, otherwise continue. Next, perform linear search for element b; if it is found, return its index, otherwise continue. Last, perform linear search for element c; if it is found, return its index, otherwise return -1. What is the best big O estimate of the algorithm runtime?

O(3n)

O(n)

O(n3)

O(3n)