1253.cpp

#include <bits/stdc++.h>
#include <quadmath.h>

#define vt vector
#define en '\n'
#define ll long long
#define ull unsigned long long
#define ld long double
#define ioa insert_or_assign
#define umap unordered_map
#define prq priority_queue
#define pb push_back
#define pii pair<int,int>
#define sz(x) (int)(x).size()
#define all(x) (x).begin(), (x).end()
#define rev(c) (c).rbegin(), (c).rend()
#define mset(ar, val) memset(ar, val, sizeof(ar))

using namespace std;
const int INF = 0x3f3f3f3f; const int mINF = 0xc0c0c0c0;
const ll LINF = 0x3f3f3f3f3f3f3f3f; const ll mLINF = 0xc0c0c0c0c0c0c0c0;
int T = 1;

void sol() {
	int N;
	cin >> N;
	vt<int> v(N);
	for(int& x : v) cin >> x;

	int cnt = 0;
	for(int i=0; i<N; ++i) {
		int x = v[i];
		umap<int,int> um;

		for(int j=0; j<N; ++j) {
			if(i == j) continue;

			bool found = 0;
			if(um.find(x - v[j]) != um.end()) {
				cnt++;
				break;
			} else {
				um[v[j]] = x-v[j];
			}
		}
	}

	cout << cnt << en;

	return;
}


int main(){
	ios_base::sync_with_stdio(0); cin.tie(0);
	
	while(T--) {
		sol();
	}

   return 0;
}