#include <bits/stdc++.h>
int f[1003], d[300],w[300];
using namespace std;
int main()
{
	int t, m; cin >> t >> m;
	for (int i = 1; i <= m; ++i) cin>>w[i]>>d[i];
	for (int i = 1; i <=t; ++i)
		if(i>=w[1])
			f[i]=d[1];
		else
			f[i]=0;
	for (int i = 2; i <= m; ++i)
		for (int j = t; j >= 1; --j)
		{
			if (j >= w[i])
				f[j] = max(f[j - w[i]] + d[i],f[j]);
		}
	cout <<f[t];
	return 0;
}