Pero has negotiated a Very Good data plan with his internet provider. The provider will let Pero use up 
~X~ megabytes to surf the internet per month. Each megabyte that he doesn't spend in that month gets transferred to the next month and can still be spent. Of course, Pero can only spend the megabytes he actually has.
If we know how many megabytes Pero has spent in each of the first 
~N~ months of using the plan, determine how many megabytes Pero will have available in the 
~N+1~ month of using the plan.
Input Specification
The first line of input contains the integer ~X~ 
~(1 \le X \le 100)~.
The second line of input contains the integer ~N~ 
~(1 \le N \le 100)~.
Each of the following ~N~ lines contains an integer 
~P_i~ 
~(0 \le P_i \le 10\,000)~, the number of megabytes spent in each of the first ~N~ months of using the plan. Numbers ~P_i~ will be such that Pero will never use more megabytes than he actually has.
Output Specification
The first and only line of output must contain the required value from the task.
Sample Input 1
10
3
4
6
2
Sample Output 1
28
Explanation for Sample Output 1
In the first month, out of 
~10~ total megabytes, Pero has spent 
~4~ and transferred 
~6~ into the next month. In the second month, out of 
~16~ 
~(10+6)~ total megabytes, Pero has spent ~6~ and transferred ~10~. In the third month, out of 
~20~ 
~(10+10)~ total megabytes, Pero has spent 
~2~ and transferred 
~18~. In the fourth month, he had a total of 
~28~ megabytes to spend.
Sample Input 2
10
3
10
2
12
Sample Output 2
16
Sample Input 3
15
3
15
10
20
Sample Output 3
15
Comments
Why the second sample output 16 instead of 6?
We are looking for how many megabytes he will have available during month N+1, not just how many megabytes are unused and will be transferred.
I wish this was me in real life...