import java.util.Scanner;
public class Main {
    static int T ;
    static int n ; 
    static int[] time ;
    static int[] price ;
    static int ans ;
    static int[] dp;

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        T = sc.nextInt();
        n = sc.nextInt();
        
        time = new int[n+1];
        price = new int[n+1];
        dp = new int[T+1];
        
        for (int i = 1; i <= n; i++) {
            time[i] = sc.nextInt();
            price[i] = sc.nextInt();
        }
        
        for (int i = 1; i <= n; i++) {
            for (int j = T; j >= time[i]; j--) {
                if (j >= time[i]) {
                    dp[j] = Math.max(dp[j], dp[j-time[i]]+price[i]);
//                  System.out.println(j + ":" + dp[T]);
                }
            }
        }
        System.out.println(dp[T]);
        

    }


}