Codeforces 466 - A problem solution

A. Cheap Travel

time limit per test 1 second

memory limit per test 256 megabytes

input standard input

output standard output

Ann has recently started commuting by subway. We know that a one ride subway ticket costs a rubles. Besides, Ann found out that she can buy a special ticket for m rides (she can buy it several times). It costs b rubles. Ann did the math; she will need to use subway n times. Help Ann, tell her what is the minimum sum of money she will have to spend to make n rides?

Input

The single line contains four space-separated integers n, m, a, b (1 ≤ n, m, a, b ≤ 1000) — the number of rides Ann has planned, the number of rides covered by the m ride ticket, the price of a one ride ticket and the price of an m ride ticket.

Output

Print a single integer — the minimum sum in rubles that Ann will need to spend.

Examples

input

6 2 1 2

output

6

input

5 2 2 3

output

8

Note

In the first sample one of the optimal solutions is: each time buy a one ride ticket. There are other optimal solutions. For example, buy three m ride tickets.

Problem link : https://codeforces.com/problemset/problem/466/A

Solution :

• tab[]
• C++

• #include<bits/stdc++.h>
  using namespace std;
  int main()
  {
      int n,m,a,b;
      scanf("%d %d %d %d",&n,&m,&a,&b);
      printf("%d",min((n/m)*b+min((n%m)*a,b),a*n));
      return 0;
  }