#define _USE_MATH_DEFINES
#include <algorithm>
#include <cstdio>
#include <functional>
#include <iostream>
#include <cfloat>
#include <climits>
#include <cstring>
#include <cmath>
#include <map>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <time.h>
#include <vector>
using namespace std;

typedef long long ll;
typedef unsigned long long ull;
typedef pair<int, int> i_i;
typedef pair<ll, int> ll_i;
typedef pair<double, int> d_i;
typedef pair<ll, ll> ll_ll;
typedef pair<double, double> d_d;
struct edge { int u, v; ll w; };

ll MOD = 1000000007;
ll _MOD = 1000000009;
int INF = INT_MAX / 2;
double EPS = 1e-10;

int main() {
    int n, m;
    while (cin >> n >> m) {
        int mini = INF;
        while (m--) {
            int a, b; cin >> a >> b;
            mini = min(mini, (n + a - 1) / a * b);
        }
        cout << mini << endl;
    }
}