import java.util.*;
public class Kattis {
public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
double costPerSQMeter = Double.parseDouble(sc.nextLine());
int lawns = Integer.parseInt(sc.nextLine());
double total= 0;
for(int i = 0; i < lawns; i++){
String[] split = sc.nextLine().split(" ");
total += (costPerSQMeter * (Double.parseDouble(split[0]) * Double.parseDouble(split[1])));
}
System.out.println(total);
}
}