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: Wrong Answer)

import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		String N = scan.next();
		String K = scan.next();
        String X = scan.next();
        String Y = scan.next();
        
        int shukuhakuK = Integer.parseInt(K);
        int money1 = 0;
        int kingakuX = Integer.parseInt(X);
        int shukuhakuN = Integer.parseInt(N);
        int amari = shukuhakuN - shukuhakuK;
        int money2 = 0;
        int kingakuY = Integer.parseInt(Y);
        
        for(int i = 1; i <= shukuhakuK; i++) {
        	money1 += kingakuX;
        }for(int j = 1; j <= amari; j++) {
        	money2 += kingakuY;
        }
        System.out.println(money1 + money2);
	}
}