It's Christmas Eve, and Anna and Elsa are making dinner for their ~N~ friends! They want to surprise everybody with their favourite holiday dish: Christmas pudding, but they don't know how many to make. Anna knows that ~A~ of their friends will eat ~a_i~ Christmas puddings, while Elsa knows that the rest will eat ~b_i~ Christmas puddings. Can you help them?

Constraints

~1 \le N, a_i, b_i \le 4 \times 10^4~

~ 1 \le A \le N~

Input Specification

The first and only line will contain integers ~N, A, a_i,~ and ~b_i~.

Output Specification

Output the number of Christmas puddings Anna and Elsa need to make.

Sample Input

10 4 2 3

Sample Output

26