//丹阳新区实小路彦

include[HTML_REMOVED]

using namespace std;

int v[100005], w[100005], f[100005], n, m;

int main()
{
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 = m; j >= v[i]; j–)
f[j] = max(f[j], f[j - v[i]] + w[i] * v[i]);
cout << f[m] << endl;
return 0;
}