using namespace std;
#include <iostream>
#include <cmath>
#include <stdio.h>

int main() {

    double cost;
    cin >> cost;
    int n;
    cin >> n;

    double area = 0;
    for (int i=0; i<n; i++) {
        double len, width;
        cin >> len >> width;
        area += (len*width);
    }

    printf("%.9f\n", area*cost);
    return 0;
}