#include <bits/stdc++.h>
using namespace std;
#define fi first
#define se second
#define pb push_back
#define mp make_pair
#define int long long
typedef pair<int, int> ii;
const int N = 2e3 + 5;
const int inf = 1e14;
int n, dp[N][N];
ii a[N];
signed main() {
cin.tie(0), ios_base::sync_with_stdio(0);
cin >> n;
for(int i = 1; i <= n; i++)
cin >> a[i].fi >> a[i].se;
sort(a + 1, a + 1 + n);
for(int i = 0; i < N; i++) {
for(int j = 0; j < N; j++)
dp[i][j] = -inf;
}
dp[0][0] = 0;
for(int i = 0; i < n; i++) {
for(int j = 0; j <= n; j++) {
if(dp[i][j] == -inf) continue;
dp[i + 1][j] = max(dp[i + 1][j], dp[i][j]);
if(a[i + 1].fi == 0)
dp[i + 1][j + 1] = max(dp[i + 1][j + 1], dp[i][j] + a[i + 1].se);
if(a[i + 1].fi)
dp[i + 1][max(j - a[i + 1].fi + 1, 1ll)] = max(dp[i + 1][max(j - a[i + 1].fi + 1, 1ll)], dp[i][j] + a[i + 1].se);
}
}
cout << max(dp[n][1], 0ll);
}
