#include <iostream>
#include <set>
using namespace std;
int countSpecialElements(int a[], int n) {
set<int> s;
int cnt = 0;
for (int i = 0; i < n; ++i) {
for (int j = 0; j < i; ++j) {
if (s.count(a[i] - a[j]) || s.count(a[i] + a[j])) {
++cnt;
break;
}
}
for (int j = 0; j <= i; ++j) {
s.insert(a[i] + a[j]);
}
}
return cnt;
}
int main() {
int n;
cin >> n;
int a[n];
for (int i = 0; i < n; ++i) cin >> a[i];
cout << countSpecialElements(a, n);
return 0;
}
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