codeforce 455A—— DP—— Boredom

Description
Alex doesn't like boredom. That's why whenever he gets bored, he comes up with games. One long winter evening he came up with a game and decided to play it.
Given a sequence a consisting of n integers. The player can make several steps. In a single step he can choose an element of the sequence (let's denote it ak) and delete it, at that all elements equal to ak + 1 and ak - 1 also must be deleted from the sequence. That step bringsak points to the player.
Alex is a perfectionist, so he decided to get as many points as possible. Help him.
Input
The first line contains integer n (1 ≤ n ≤ 105) that shows how many numbers are in Alex's sequence.
The second line contains n integers a1, a2, ..., an (1 ≤ ai ≤ 105).
Output
Print a single integer — the maximum number of points that Alex can earn.
Sample Input
Input

2
1 2

Output

2

Input

3
1 2 3

Output

4

Input

9
1 2 1 3 2 2 2 2 3

Output

10

Hint
Consider the third test example. At first step we need to choose any element equal to 2. After that step our sequence looks like this [2, 2, 2, 2]. Then we do 4 steps, on each step we choose any element equals to 2. In total we earn 10 points.

#include<cstdio>

#include<cstring>

#include<algorithm>

using namespace std;

long long  dp[100010][2];

int a[100010];

int temp[100010];

int n;

int main()

{

      while(~scanf("%d", &n)){

          memset(dp, 0, sizeof(dp));

        for(int i = 1; i <= n; i++){

            scanf("%d", &a[i]);

            temp[a[i]]++;

        }



        dp[1][1] = temp[1];

        dp[1][0] = 0;

        for(int i = 2; i <= 100000; i++){

            dp[i][1] = dp[i-1][0] + 1ll*temp[i]*i;

            dp[i][0] = max(dp[i-1][1], dp[i-1][0]);

        }



        printf("%lld
", max(dp[100000][1], dp[100000][0]));

    }

    return 0;

}