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>
#include<stdlib.h>
#include<string.h>
typedef long long ll;
int main(){
    int n,k,y,x;
    while(scanf("%d",&n)!=EOF){
        scanf("%d",&k);
        scanf("%d",&x);
        scanf("%d",&y);
        ll sum = 0;
        if(n>=k){
            for(int i=1; i<=k; i++){
            sum +=x;
        }
            for(int i=k+1; i<=n; i++){
                sum +=y;
            }
        }
        else if(n<k){
            for(int i=0; i<n; i++){
                sum += x;
            }
        }
        printf("%lld\n",sum);

        }




    return 0;
}