#include <iostream>
#include <vector>
#include <algorithm>
#include <math.h>

using namespace std;

int main(){

    int eggs;
    int n;
    vector<int> prices;


    cin >> eggs;
    cin >> n;


    for(int i=0; i < n; i++){

        int temp;
        int tempt;

        cin >> temp >> tempt;

        int oneegg = tempt * eggs;
        int tomultiply = round(eggs / 6);
        int sixeggs = tomultiply * temp;

        prices.push_back(sixeggs);
        prices.push_back(oneegg);

    }

    sort(prices.begin(),prices.end());

    cout << prices[0] << "\n";

}