#include <bits/stdc++.h>
using namespace std;
const int N = 1e5 + 10;
int t,m,w[N],c[N],dp[N][2000];
int main(){
	cin >> t >> m;
	for(int i = 1;i <= m;i++){
		cin >> w[i] >> c[i];
	}
	for(int i = 1;i <= m;i++){
		for(int j = 1;j <= t;j++){
			if(w[i] > j){
				dp[i][j] = dp[i - 1][j];
			}else{
				dp[i][j] = max(dp[i - 1][j],dp[i - 1][j - w[i]] + c[i]);
			}
		}
	}
	cout << dp[m][t];
	return 0;
}