8370번 - Plane 다국어

Byteland Airlines recently extended their aircraft fleet with a new model of a plane. The new acquisition has n₁ rows of seats in the business class and n₂ rows in the economic class. In the business class each row contains k₁ seats, while each row in the economic class has k₂ seats.

Write a program which:

• reads information about available seats in the plane,
• calculates the sum of all seats available in that plane,
• writes the result.

In the first and only line of the standard input there are four integers n₁, k₁, n₂ and k₂ (1 ≤ n₁, k₁, n₂, k₂ ≤ 1 000), separated by single spaces.

The first and only line of the standard output should contain one integer - the total number of seats available in the plane.