Time limit: 5000ms
Memory limit: 256mb

Description:
In a museum, there is a infra-red sensor at the door scanning the the ID of visitors, which is recorded each time a visitor enters or leaves the museum. Given a series of IDs recorded in a day, your task is to determine whether every visitor has left the museum. Assume nobody is inside the museum at the beginning.

-------------------------Copy the following code, complete it and submit-------------------------

/*
I, <Your Full Name>, am submitting the assignment for
an individual project.
I declare that the assignment here submitted is original except for
source material explicitly acknowledged, the piece of work, or a part
of the piece of work has not been submitted for more than one purpose
(i.e. to satisfy the requirements in two different courses) without
declaration. I also acknowledge that I am aware of University policy
and regulations on honesty in academic work, and of the disciplinary
guidelines and procedures applicable to breaches of such policy and
regulations, as contained in the University website
http://www.cuhk.edu.hk/policy/academichonesty/.
It is also understood that assignments without a properly signed
declaration by the student concerned will not be graded by the
teacher(s).
*/

#include <stdio.h>
#include <stdlib.h>

struct Entry{
    int ID;
    int isInside;
};

void init_hashTable(struct Entry hashTable[], int hashTableSize){
    for (int i = 0; i < hashTableSize; i++){
        hashTable[i].ID = -1;
        hashTable[i].isInside = 0;
    }
}

int hashFunc1(int x, int hashTableSize){
    return x % hashTableSize;
}

int hashFunc2(int x){
    return x % 29 + 1;
}

int doubleHashFunc(int x, int i, int hashTableSize){
    return (hashFunc1(x,hashTableSize) + i * hashFunc2(x)) % hashTableSize;
}

int search(int x, struct Entry hashTable[], int hashTableSize){
    // write your code here
}

void insert(int x, struct Entry hashTable[], int hashTableSize){
    for (int i = 0; i < hashTableSize - 1; i++){
        int hashed_key = doubleHashFunc(x,i,hashTableSize);
        if(hashTable[hashed_key].ID == -1){
            // write your code here
        }
    }
}

int main(void) {
    int id;
    int numInside = 0;
    int hashTableSize = 29989;
    struct Entry hashTable[hashTableSize];
    init_hashTable(hashTable,hashTableSize);
    while(scanf("%d",&id) != EOF){
        if (id == -1) {
            break;
        }
        int hashed_key = search(id, hashTable, hashTableSize);
        if(hashed_key != -1){
            if(hashTable[hashed_key].isInside){
                numInside -= 1;
            }
            else{
                numInside += 1;
            }
            hashTable[hashed_key].isInside = 1 - hashTable[hashed_key].isInside;
        }
        else{
            insert(id, hashTable, hashTableSize);
            numInside += 1;
        }
    }
    printf("%d\n",numInside);
    return 0;
}


-------------------------------------------End of Code-------------------------------------------

Input:
N lines of ID: M_1, M_2, ..., M_N.
0 <= N <= 10000; 1 <= M_i <= 2^31-1; 
Finally, input -1 as the end symbol.

Output
Output the number of the people that are still inside the museum.

Sample Input 1:
2
5
2
7
9
-1

Sample Output 1:
3

Sample Input 2:
1
385
9999
385
385
9999
1
385
-1

Sample Output 2:
0