import java.io.*;
import java.util.*;

public class Main {
    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner();
        int count =  sc.nextInt() * (sc.nextInt() - sc.nextInt());
        int price = sc.nextInt();
        int avg = sc.nextInt();
        long ans = 0;
        for (int i = 1; i <= count; i++) {
            if (i % 10 == 0) {
                if (avg <= price) {
                    price -= avg;
                }
            }
            ans += price;
        }
        System.out.println(ans);
    }
}
class Scanner {
    BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
    StringTokenizer st = new StringTokenizer("");
    
    public Scanner() throws Exception {
        
    }
    
    public int nextInt() throws Exception {
        return Integer.parseInt(next());
    }
    
    public long nextLong() throws Exception {
        return Long.parseLong(next());
    }
    
    public String next() throws Exception {
        if (!st.hasMoreTokens()) {
            st = new StringTokenizer(br.readLine());
        }
        return st.nextToken();
    }
}