Problems

# School Olympiad

# School Olympiad

At school programming contest the participants were asked to solve two problems. **a** students totally coped with the given tasks, and **b** students solve nothing.

How many participants were in competition if there was accepted **c** correct submitions for the first task, and **d** submitions for the second task.

#### Input

Nonnegative integers **a**, **b**, **c** и **d**, not greater than **100**.

#### Output

Number of participants at school programming contest.

Input example #1

1 2 3 4

Output example #1

8