466A - Cheap Travel.cpp

/*
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
inputCopy
6 2 1 2
outputCopy
6
inputCopy
5 2 2 3
outputCopy
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.
*/




#include<bits/stdc++.h>
using namespace std;

int main(){
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    
    int n, m, a, b;
    cin >> n >> m >> a >> b;
    
    int single = n * a;
    int multiple = ceil((float)n / m) * b;
    int mix = (n / m) * b + (n % m) * a;
    
    cout << min(single, min(multiple, mix));
    
    
    return 0;
}