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: Wrong Answer)

#include <stdio.h>

int main ()
{
  int i, n, k, x, y, so, ad;
  scanf ("%d %d %d %d",&n,&k,&x,&y);
  for (i = 1; i <= n; i++)
{
      
if (n>k)
{
    
     for (i = 1; i <= k; i++)
	{
	  so += x;
	}

      for (i = 1; i <= n - k; i++)
	{
	  ad += y;
	}

      printf ("%d", so + ad);
      break;
  }
       
if(k>n)
{
       
        for (i = 1; i <= n; i++)
	{
	  so += x;
	}

      printf ("%d", so );
      break;
}


}

  return 0;
}