Reward ( DHBB - LQDOJ )

#include <iostream>
#include <vector>
#include <algorithm>
#include <numeric>
#include <cmath>
#include <queue>
using namespace std;
const int N = 1e4;
int a[2*N + 1], b[N+1], n;
long long dp[N+1];
void read()
{
   cin >> n;
   fill (b + 1, b + N + 1, 0);
   for (int i = 1; i <= n; ++ i)
   {
       cin >> a[i];
       ++b[a[i]];
   }
}
void solve()
{
   dp[1] = b[1];
   for (int i = 2; i <= N; ++ i)
   {
       dp[i] = max(dp[i-2] + b[i]*i, dp[i-1]);
   }
   cout << dp[N];
}
int main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    read();
    solve();
}