C++ :

#include<iostream>
using namespace std;
int main(){
    const int penKinds = 3;   
    int penAmount,penPrice;    
    int minCost = 0;        
    int n;                   
    cin>>n;                    
    for(int i = 0;i < penKinds;i++){
        cin>>penAmount>>penPrice;
        int penCost = (n/penAmount)*penPrice;
        if(n%penAmount != 0)
            penCost += penPrice;
        if(i == 0 || (i != 0 && penCost < minCost))
            minCost = penCost;
    }
    cout<<minCost;
    return 0;
}

Java :

import java.util.Scanner;
import java.util.Arrays;

public class Main{
	public static void main(String[] args){
		Scanner scan = new Scanner(System.in);
		int n = scan.nextInt();
		int a1 = scan.nextInt();
		int a2 = scan.nextInt();
		int b1 = scan.nextInt();
		int b2 = scan.nextInt();
		int c1 = scan.nextInt();
		int c2 = scan.nextInt();
		int pen1 = 0, pen2 = 0, pen3 = 0;
		int[] array = new int[4];
		while(pen1 < n){
			pen1 = pen1 + a1;
			array[0] = array[0] + a2;
		}
		while(pen2 < n){
			pen2 = pen2 + b1;
			array[1] = array[1] + b2;
		}
		while(pen3 < n){
			pen3 = pen3 + c1;
			array[3] = array[3] + c2;
		}
		Arrays.sort(array);
		System.out.println(array[1]);
	}
}