#include <iostream>
#include <algorithm>
#define rep(i, a, b) for (int i = a; i <= b; i++)
using namespace std;
int V, n;
struct Node {
    int a;
    int b;
    bool operator<(Node node) { return this->b > node.b; }
} list[200005];

int main() {
    ios::sync_with_stdio(false);
    cin >> V >> n;
    rep(i, 1, n) { cin >> list[i].a >> list[i].b; }
    sort(list + 1, list + n + 1);
    int cnt = 0;
    int result = 0;
    rep(i, 1, n) {
        rep(j, 1, list[i].a) {
            if (cnt < V) {
                cnt++;
                result += list[i].b;
            }
        }
    }
    cout << result;
}