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++14 (GCC 5.4.1) (judge verdict: Wrong Answer)

#include <stdio.h>
#include <string.h>
using namespace std;

int main()
{
    char w[101];
    char t[] = "abcdefghijklmnopqrstuvwxyz";
    char res[26];
    int cnt = 0, j = 0;

    for (int i = 0; i < 101; ++i) w[i] = 0;

    scanf("%s", w);

    for (int k = 0; k < 26; ++k) {
        for (int i = 0; i < strlen(w); ++i) {
            if (w[i] == t[k]) {
                res[j] = w[i];
                ++j;
            }
        }
    }
    int len = j;

    for (int k = 0; k < 26; ++k) {
        for (j = 0; j <= len; ++j) {
            if (t[k] == res[j]) ++cnt;
        }
    }

    if (cnt % 2 == 0) printf("Yes\n");
    else printf("No\n");

    return 0;
}