Problem

You are given an array A of length N. Processing the array from left to right:

• If A[i] > 0, a group containing A[i] tickets is added to the end of a queue.
• If A[i] = 0, the earliest unprocessed group in the queue is removed, and its size is added to the score.
• If the queue is empty, nothing happens.

Find the final score.

Input

• First line: N
• Second line: N space-separated integers A[i]

Output

• Print the final score.