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>
#include<string.h>

int main(void)
{
  int i[26],flag = 0;
  char n[110];
  scanf("%s",n);
  
  for(int m = 0;m <= 26;m++)
  {
    i[m] = 0;
  }
  
  for(int m = 0;m < strlen(n);m++)
  {
    i[n[m] - 97] += 1;
  }
  
  for(int j = 0;j <= 25; j++)
  {
    if(i[j] % 2 != 0){printf("No"); return 0;}
  }
  
  printf("Yes");
  
  return 0;
}