Debts

Nowadays, children don't really like to read, so the attendance of libraries is dropping, and no one wants to modernize the library inventory system. Your acquaintance, Alice, works at the city library and asks for your help. She knows that there are currently $a$ books in the library, and Bob borrowed $b$ books and Svetlana borrowed $c$ books. Also, during this month, Dmitry will take $d$ books. Bob and Svetlana only borrowed books for one month, so they have to return them within this month. Tell Alice how many books will be in the city library next month.

Input

The first line contains one integer $a$ ($1\le a\le 100$) — the number of books that are in the city library.

The second line contains one integer $b$ ($1\le b\le 100$) — the number of books borrowed by Bob from the library.

The third line contains one integer $c$ ($1\le c\le 100$) — the number of books borrowed by Svetlana from the library.

The fourth line contains one integer $d$ ($1\le d\le 100$) — the number of books that Dmitry will take from the library.

It is guaranteed that there will be a non-negative number of books in the city library at the end.

Output

Output one integer — the answer to the problem.

Examples