板子

#include <iostream>
#include <stack>
#include <cmath>
#include <vector>
#include <string.h>
#include <queue>
#include <stdio.h>
#include <iomanip>
#include <cstdio>
#include <algorithm>
#define LL long long
#define double long double
using namespace std;
const int N = 1e5 + 10;
const int INF = 0x3f3f3f3f;
int n, m, v[N], w[N], dp[N];
signed main()
{
	cin >> n >> m;
	for(int i = 1; i <= m; i++)
	{
		cin >> v[i] >> w[i];
	}
	for(int i = 1; i <= m; i++)
	{
		for(int j = n; j >= v[i]; j--)
		{
			dp[j] = max(dp[j], dp[j - v[i]] + v[i] * w[i]);
		}
	}
	cout << dp[n] << endl;
	return 0;
}