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(){
  int al[26]={0};
  int aa[2]={0};
  int i,j;
  char w[101];
  scanf("%s",w);
  int len=strlen(w);
  for(i=0;i<len;i++){
    j=w[i]-'a';
    al[j]++;
  }
  for(i=0;i<26;i++){
    if(al[i]!=0&&al[i]%2==0){
      aa[0]++;
    }else if(al[i]!=0&&al[i]%2!=0){
      aa[1]++;
    }
  }
  if(aa[1]==0){
    printf("Yes\n");
  }else if(aa[1]!=0){
    printf("No\n");
  }
  return 0;
}