Description

In Class 2 of Grade 4 at Yucai Primary School, there are $n$ students in total. Among them, $a$ students participate in the Chinese interest group, $b$ students participate in the mathematics interest group, and $c$ students participate in both groups. How many students are not participating in either group?

Input Format

Input consists of a single line with positive integers $n$ ($0 < n \le 10000$), $a$, $b$, $c$ ($a,b,c \le n$ and $c < \min(a,b)$).

Output Format

Output the number of students who are not participating in either interest group.

Sample

46 21 18 9

16