Social networks#10226

Social networks

1 second

64 megabytes

Very easy

On Instagram, there are $A$ students registered, while on Facebook, there are $B$ students. Among these, $C$ students are registered on both social networks. Additionally, $D$ students do not use the Internet or social networks at all. Calculate the total number of students in the class.

Input

The input consists of a single line containing four integers: $A$ , $B$ , $C$ , and $D$ .

Output

Output a single number representing the total number of students in the class.

Examples

Example 1

Loading