#include <map>
#include <set>
#include <list>
#include <cmath>
#include <ctime>
#include <deque>
#include <queue>
#include <stack>
#include <bitset>
#include <cstdio>
#include <limits>
#include <vector>
#include <cstdlib>
#include <numeric>
#include <sstream>
#include <iostream>
#include <algorithm>
#include <functional> 
#include <iomanip>
#include <unordered_map>
#include <memory.h>
#include <unordered_set>
#include <fstream>
#include <random>

using namespace std;

int dp[10001];

int main(void)
{
	cin.tie(0);
	ios::sync_with_stdio(false);

	vector <pair<int, int>> v;
	int n, a, b;

	cin >> n;

	for (int i = 0; i < n; i++)
	{
		cin >> a >> b;
		v.push_back(make_pair(a, b));
	}

	sort(v.begin(), v.end());
	
	for (int i = 0; i <= n; i++)
	{
		dp[i] = -1e9;
	}
	dp[0] = 0;

	for (int i = 1; i <= n; i++)
	{
		int a = v[i - 1].first;
		int b = v[i - 1].second;
		for (int j = 0; j < i; j++)
		{
			if (dp[j] < b)
			{
				dp[i] = max(dp[i], dp[j] + a);
			}
		}
	}

	int res = 0;

	for (int i = 0; i <= n; i++)
	{
		res = max(res, dp[i]);
	}

	cout << res << '\n';

	return 0;
}