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 C (GCC 5.4.1) (judge verdict: Accepted)

#include<stdio.h>
int main()
{
    int n,k,x,y,nc,sn,snc,tc; //nc=nights_cost,sn=subsequent nights,snc=subsequent nights cost,tc=totalcost//
    scanf("%d%d%d%d",&n,&k,&x,&y);
    if(n<k)
    {
        nc=n*x;
        printf("%d\n",nc);
    }
    else
    {
    nc=k*x;
    sn=n-k;
    snc=sn*y;
    tc=nc+snc;
    printf("%d\n",tc);
    }
    return 0;
}