#include <bits/stdc++.h>
using namespace std;
using ll=long long;
ll d[2005];
int main(){
 int n;cin>>n;
 vector<int> p;
 fill(d,d+2005,LLONG_MIN);
 d[0]=0;
 for(int i=0;i<n;i++){
  int a,b;cin>>a>>b;
  if(a==0&&b>0)p.push_back(b);
  else for(int j=2004;j>=0;j--)if(d[j]!=LLONG_MIN)d[min(2004,j+max(0,a-1))]=max(d[min(2004,j+max(0,a-1))],d[j]+b);
 }
 sort(p.rbegin(),p.rend());
 for(int i=1;i<p.size();i++)p[i]+=p[i-1];
 ll r=*max_element(d,d+2005);
 for(int i=0;i<min(2004,(int)p.size());i++)r=max(r,d[i]+p[i]);
 cout<<r<<"\n";
}

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NgoyIC0zCjMgLTEKMCAtNAowIC0yCjEgLTMKNCAtMQ==

6
2 -3
3 -1
0 -4
0 -2
1 -3
4 -1