#include <bits/stdc++.h>
using namespace std;
using i64 = long long;

const int N = 30010;
int f[N];
int main()
{
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    int n,m;
    cin >> m >> n;
    for(int i = 1; i <= n; i ++ )
    {
        int v,w;
        cin >> v >> w;
        for(int j = m; j >= v; j -- )
            f[j] = max(f[j],f[j - v] + v*w);
    }
    cout << f[m] << "\n";
    return 0;  
}