#include <iostream>

using namespace std;
const int N = 510,M = 503;
int d[M];
int n;

int find(int x){
    int idx = (x % M + M) % M;
    while(d[idx] && d[idx] != x){
        idx++;
        if(idx == M) idx = 0;
    }
    return idx;
}

int main(){
    cin >> n;
    int res = 0;
    for(int i = 0;i < n;i++){
        int temp;
        cin >> temp;
        if(temp < 0) temp = -temp;
        int dix = find(temp);
        if(d[dix] == temp) res++;
        else d[dix] = temp;
    }
    cout << res << endl;
    return 0;
}