It's the middle of December, so Daniel is preparing for a relaxing summer! (Hey, it's summer somewhere in the world). He's planning on taking a 2-week vacation to spend some time with his friends and family, and to take his mind off work.

Daniel wants to invite all of his ~N~ friends over for a secret santa. Unfortunately, some of his friends are out of town, with plans to go to the beach and amusement park.

~A~ friends have plans to go to the beach, ~B~ friends have plans to go to the amusement park, and ~C~ of the friends going to either one of the beach or amusement park have plans to go to both.

How many friends can Daniel invite?

Constraints

~1 \le N \le 10^9~

~C \le A+B~

Input Specification

The first and only line of input contains four integers, ~N~, ~A~, ~B~, and ~C~.

Output Specification

Output one integer, the number of friends that are in town with no plans.

Sample Input

9 3 2 1

Sample Ouput

5