John managed to get a great internet plan for his cell phone. The plan allows John to use a quota of up to X megabytes of data per month to surf the Internet. If John doesn't use all of his quota in a month, the unused megabytes are added to the next month's quota. According to the contract, John can never use more megabytes than his current quota.

In this problem, you are given the value of the monthly quota X and the number of megabytes that John used in each of the first N months of the plan. Your task is to determine how many megabytes John has left to use in month N+1.

For example, if X = 200 megabytes and John used 150 megabytes in the first month and 220 megabytes in the second month, then in the third month John has a quota of 230 megabytes (50 megabytes are carried over from the first to the second month, 30 megabytes are carried over from the second to the third month).

Input: Integer (int) and list of integers.

Output: Integer (int).

assert internet_quota(200, [150, 220]) == 230
assert internet_quota(100, [50, 80, 30]) == 240
assert internet_quota(150, [120]) == 180