#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
template<class T> bool maximize(T &a, const T &b){ return (a < b ? a = b, 1 : 0); }
template<class T> bool minimize(T &a, const T &b){ return (a > b ? a = b, 1 : 0); }
#define fi first
#define se second
#define pb push_back
#define ii pair<int, int>
#define all(x) x.begin(), x.end()
#define TASK "nonsense"
/// end of template ///
const int N = 2e3 + 10;
const int inf = INT_MAX-10;
struct Strap
{
int a,b;
Strap() {}
void input()
{
cin>>a>>b;
--a;
}
bool operator < (const Strap &S) const
{
if(a!=S.a) return a>S.a;
return b>S.b;
}
} strap[N];
int n,dp[N][N];
void solve()
{
cin>>n;
for(int i=1;i<=n;++i) strap[i].input();
sort(strap+1,strap+1+n);
for(int i=0;i<N;++i) for(int j=0;j<N;++j) dp[i][j]=-inf;
dp[0][1]=0;
int ans=-inf;
for(int i=0;i<=n;++i) for(int j=1;j<=n;++j) if(dp[i][j]!=-inf)
{
if(strap[i].a>=0)
{
if(i==n || strap[i+1].a<0)
{
int sum=dp[i][j];
for(int pos=i+1;pos<=min(n,i+j);++pos) sum+=max(0,strap[pos].b);
maximize(ans,sum);
}
else
{
maximize(dp[i+1][min(n,j+strap[i+1].a)],dp[i][j]+strap[i+1].b);
maximize(dp[i+1][j],dp[i][j]);
}
}
}
cout<<ans;
}
int main() {
ios_base::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
// freopen(TASK".inp","r",stdin);
// freopen(TASK".out","w",stdout);
int testcase=1;
// cin>>testcase;
while (testcase--)
solve();
return 0;
}
