backpack v1

#include <iostream>

using namespace std;

int main() {
    int c;
    double n, item, price, sum = 0;
    cin >> n;
    cin >> c;
    double a[c][3];
    for (int i = 0; i < c; i++) {
        cin >> item;
        a[i][0] = item;
        cin >> price;
        a[i][1] = price;
        a[i][2] = price / item;
    }
    for (int i = 0; i < c - 1; i++) {
        for (int j = 0; j < c - i - 1; j++) {
            if (a[j][2] < a[j+1][2]) {
                double t = a[j+1][2];
                a[j+1][2] = a[j][2];
                a[j][2] = t;
                double t1 = a[j+1][0];
                a[j+1][0] = a[j][0];
                a[j][0] = t1;
            }
        }
    }


    for (int i = 0; ; i++) {
        if (n > a[i][0]) {
            sum += a[i][0] * a[i][2];
            n -= a[i][0];
        } else {
            sum += n * a[i][2];
            break;
        }

    }

    cout << sum;

    return 0;
}