#include<fstream>
#include<string.h>
#include<ctype.h>
#include<iostream>
#include<algorithm>
#include<map>
#include<unordered_map>
#include<array>
#include<deque>
#include<unordered_set>
#include<set>
#include<math.h>
using namespace std;
int n, dp[111111], i, a, b, val, el, prvval, j, anteval, ok, max1;
map<int, bool>mp[111111];
map<int, bool>::iterator iter;
set<int>final;
set<int>::iterator it;
int main()
{
	ifstream f("heavymetal.in");
	ofstream g("heavymetal.out");
	f >> n;
	for (i = 1; i <= n; i++)
	{
		f >> a >> b;
		mp[b][a]==1;
		final.insert(b);
	}
	it = final.begin();
	val = 1;
	while (it != final.end())
	{
		while (val != *it)
		{
			dp[val] = dp[val - 1];
			val++;
		}
		val++;
		iter = mp[*it].begin();
		while (iter != mp[*it].end())
		{
			dp[*it] = max(dp[*it], dp[*it - (iter->first)] + *it - iter->first);
			iter++;
		}
		it++;
	}
	it--;
	g << dp[*it];
	return 0;
}