#include<bits/stdc++.h>
#define int long long
using namespace std;
const int N=2010;
int n,ans,id;
int dp[N],f[N][N];
signed main()
{
	cin>>n;
	memset(f,128,sizeof(f));
	f[0][0]=0;
	for(int i=1;i<=n;i++)
	{
		int x,y;
		cin>>x>>y;
		if(x==0)
		{
			for(int j=n;j>=1;j--)
				dp[j]=max(dp[j],dp[j-1]+y);
		}
		else
		{
			x--;
			if(x==0)
			{
				ans+=max(y,0ll);
				continue;
			}
			id++;
			for(int j=x;j<=n;j++)
				f[id][j]=f[id-1][j]+y;
			for(int j=x;j<=n;j++)
				f[id][j]=max(f[id][j],f[id-1][j-x]+y);
		}
	}
	dp[n+1]=dp[n];
	int ma=0;
	for(int i=0;i<=n;i++)
		ma=max(ma,f[id][i]+dp[i+1]);
	cout<<ma+ans;
	return 0;
}