#include<iostream>
using namespace std;
const int N = 30, M = 30010;
int f[N][M], w[N], v[N];

int main()
{
    int n, m;
    cin >> m >> n;
    for(int i = 1;i <= n; i++) cin >> v[i] >> w[i];

    for(int i = 1; i <= n; i++)
    {
        for(int j = 1; j <= m; j++)
        {
            f[i][j] = f[i - 1][j];
            if(v[i] <= j) f[i][j] = max(f[i][j], f[i - 1][j - v[i]] + w[i] * v[i]);
        }

    } 

    cout << f[n][m] << endl;
    return 0;
}