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User's AC Ratio

100.0% (2/2)

Submission's AC Ratio

33.3% (4/12)

Description

There are M male students, N female students, and a teacher in a classroom.
The teacher wants to compute the total amount of money in the classroom by a "reduction" procedure.
A student tells his/her amount of money to another student (or to the teacher).
The receiver computes the sum, and relay the information to the next receiver.

For the reduction procedure:
Everyone can only speak to one person, everyone can only listen to one person,
and no one can speak and listen at the same time.

It takes A seconds for a female student to tell a number, and B seconds for a male student.

Given A, B, N, M, find the least time if there is a way to do this.

Input Format

There are four numbers A, B, N, M. For all test cases, 1<=A<B<=10000 and 0<=N,M<=200

Output Format

Output the least amount of time.

Sample Input

3 5 2 1

Sample Output

8

Hints

Problem Source

原TIOJ1534 / ACP 2009 期末考前練習。 Problem setter: Tmt.

Subtasks

No. Testdata Range Score
1 0 7
2 1 7
3 2 7
4 3 7
5 4 7
6 5 7
7 6 7
8 7 7
9 8 7
10 9 7
11 10 7
12 11 7
13 12 16

Testdata and Limits

No. Time Limit (ms) Memory Limit (KiB) Output Limit (KiB) Subtasks
0 5000 65536 262144 1
1 5000 65536 262144 2
2 5000 65536 262144 3
3 5000 65536 262144 4
4 5000 65536 262144 5
5 5000 65536 262144 6
6 5000 65536 262144 7
7 5000 65536 262144 8
8 5000 65536 262144 9
9 5000 65536 262144 10
10 5000 65536 262144 11
11 5000 65536 262144 12
12 5000 65536 262144 13