#include<iostream>#include<cstdio>#include<algorithm>using namespace std;int fun(int x){    return x>0?x:-x;}bool cmp(int a,int b){    return fun(a)<fun(b);}int main(){    int n,a[505];    cin >> n;    for(int i = 1;i <= n;i++)    {        cin >> a[i];    }    sort(a+1,a+n+1,cmp);    int num = 0;    for(int i = 1;i < n;i++)    {        if(fun(a[i]) == fun(a[i+1]))        {            num++;            i++;        }    }    cout << num << endl;    return 0;}