#include<bits/stdc++.h>
using namespace std;
const int N = 1000 + 10;
int m , w[N] , c[N] , dp[1010] , n;
int main(){
	cin >> m >> n;
	for(int i = 1;i <= n;i++)
	    cin >> w[i] >> c[i];
	for(int i = 1;i <= n;i++)
        for(int j = w[i];j >= m;j++) 
        	dp[j] = max(dp[j] , dp[j - w[i]] + c[i]);
	cout << dp[m];
	return 0;
}