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 Go (1.6) (judge verdict: Accepted)

package main

import(
    "fmt"
)



func main() {
    var n,k,x,y int
    fmt.Scan(&n,&k,&x,&y)
    fmt.Println(min32(n,k)*x + max32(n-k,0)*y)
}





func min32(a, b int) int {
    if a >= b {
        return b
    }
    return a
}

func max32(a, b int) int {
    if a >= b {
        return a
    }
    return b
}

func min64(a, b int64) int64 {
    if a >= b {
        return b
    }
    return a
}

func max64(a, b int64) int64 {
    if a >= b {
        return a
    }
    return b
}

func gcd(a, b int64) int64 {
    if a % b == 0 {
        return b
    } else {
        return gcd(b, a%b)
    }
}

func lcm(a, b int64) int64 {
    return a / gcd(a, b) * b
}