#include<iostream>
#include<cmath>
#include<cstring>
typedef long long LL;
using namespace std;
int f[1000005], c[15], w[15];
LL s, n, d;
int main()
{
	cin >> s >> n >> d;
	for (int i = 1; i <= d; i++)
	{
		cin >> c[i] >> w[i];
		c[i] /= 1000;
	}
	for (int q = 1; q <= n; q++)//每一年
	{
		//memset(f, 0, sizeof(f));//初始化；我没有写也可以过？？？
		LL h = s / 1000;
		for (int i = 1; i<= d; i++)//当年最大值的选法；
		{
			for (int j = c[i]; j <= h; j++)
				f[j] = max(f[j], f[j - c[i]] + w[i]);
		}
		s += f[h];
	}
	cout << s << endl;
	return 0;
}