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 JavaScript (node.js v5.12) (judge verdict: Accepted)

function Main(input) {
	input = input.trim();
	//input = input.trim().split(" ");
	//input = input.trim().split("\n");
	//input = input.trim().split(" ").map((a)=>Number(a));
	input = input.trim().split("\n").map((a)=>Number(a));
  var N = input[0];
  var K = input[1];
  var X = input[2];
  var Y	= input[3];
  console.log(X * Math.min(N,K) + Math.max(0,N - K) * Y);
}

Main(require("fs").readFileSync("/dev/stdin", "utf8"));