#include <bits/stdc++.h>
using namespace std;
int main()
{
	int n, m;
	cin >> n >> m;
	long long value[m], mess[m], t;
	for (int i = 0; i < m; i++)
	{
		cin >> mess[i] >> t;
		value[i] = mess[i] * t;
	}
	long long ts[n + 1] = {};

	for (int j = 0; j < m; j++)
	{
		for (int i = n - 1; i >= 0; i--)
		{

			if (mess[j] <= i)
				ts[i] = max(ts[i - mess[j]] + value[j], ts[i - 1]);
		}
	}

	cout << ts[n - 1];
}

样例过了，但是评测70分。