Problem:
Score : 100 points

Problem Statement

There is a hotel with the following accommodation fee:

X yen (the currency of Japan) per night, for the first K nights

Y yen per night, for the (K+1)-th and subsequent nights

Tak is staying at this hotel for N consecutive nights.
Find his total accommodation fee.

Constraints

1 \leq N, K \leq 10000

1 \leq Y < X \leq 10000

N,\,K,\,X,\,Y are integers.

Input

The input is given from Standard Input in the following format:

N
K
X
Y

Output

Print Tak's total accommodation fee.

Sample Input 1

5
3
10000
9000

Sample Output 1

48000

The accommodation fee is as follows:

10000 yen for the 1-st night

10000 yen for the 2-nd night

10000 yen for the 3-rd night

9000 yen for the 4-th night

9000 yen for the 5-th night

Thus, the total is 48000 yen.

Sample Input 2

2
3
10000
9000

Sample Output 2

20000

Solution in Java8 (OpenJDK 1.8.0) (judge verdict: Accepted)

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class Main {

	public static void main(String[] args) throws IOException {
		BufferedReader input =new BufferedReader (new InputStreamReader (System.in));
		String strn = input.readLine( );
		int n = Integer.parseInt(strn);
		String strk = input.readLine( );
		int k = Integer.parseInt(strk);
		String strx = input.readLine( );
		int x = Integer.parseInt(strx);
		String stry = input.readLine( );
		int y = Integer.parseInt(stry);

		int answer = 0;


		if(n>k){
			for(int i=0; i<k; i++){
				answer = answer + x;
			}
			for(int i=k; i<n; i++){
				answer = answer + y;
			}
		}else{
			for(int i=0; i<n; i++){
				answer = answer + x;
			}
		}

		System.out.println(answer);
	}

}