#include <bits/stdc++.h>
using namespace std;
const int N = 100 + 5 , M = 5e6 + 5;
int dp[M] , v[M] , w[M];
int main()
{
	int m , n , T; cin >> m >> T >> n ;
	for(int i = 1;i <= n;i++) cin >> v[i] >> w[i];
	for(int i = 1;i <= n;i++)
	{
		for(int j = v[i];j <= 5e6;j++)
		{
			dp[j] = max(dp[j] , dp[j-v[i]]+w[i]);
		}
	}
	while(T--)
	{
		m += dp[m];
	}
	cout << m << endl;
	return 0;
}