#include<iostream>
#include<vector>
#include <algorithm>
#include<queue>
using namespace std;
struct node
{
	int p,d;
		node(){p=0;d=0;}
};
class Supermarket
{
public:
	void input(int);
	void solve();
private:
	priority_queue<int>schedule[10001];
	vector<int> num;
	vector<int> deadline;
	int N,m;
};
void Supermarket::input(int n)
{
	int i,j=1,px,dx;
	node tt;
	N=n;
	num.assign(n+1,0);
	deadline.assign(n+1,0);
	for(i=1;i<=n;i++)
	{
		scanf("%d%d",&px,&dx);
		tt.d=dx;
		tt.p=px;
		if(schedule[dx].empty())
			deadline[j++]=dx;
	    schedule[dx].push(tt.p);	
	}
	m=j;
	sort(deadline.begin(),deadline.begin()+j);
}
void Supermarket::solve()
{
	int i,l=1,j=1,t,k,sum;
	i=deadline[l];
	for(j=1;j<=N;j++)
	{
		k=j;
		sum=0;
	   	while(!schedule[i].empty())
		{
             t=deadline[k];
			if(t==0)
			{
				while(!schedule[i].empty())
				{
					schedule[i].pop();
				}
				break;
			}
		    while(t>deadline[k-1]&&!schedule[i].empty())
			{
		        sum+=schedule[i].top();
		    	schedule[i].pop();
                t--;
			}
            if(num[k-1]+sum>num[j])
			{
			    num[j]=num[k-1]+sum;
			}
			k--;
		}
		i=deadline[++l];
	}
	//printf("\n");
	printf("%d\n",num[m-1]);
}
int main()
{
	int n;
	while(scanf("%d",&n)!=EOF)
	{
		Supermarket bb;
		bb.input(n);
		bb.solve();
	}
	return 0;	
}