#include "bits/stdc++.h" using namespace std; #define REP(i, n) for(ll i = 0;i < n;i++) #define REPR(i, n) for(ll i = n;i >= 0;i--) #define FOR(i, m, n) for(ll i = m;i < n;i++) #define FORR(i, m, n) for(ll i = m;i >= n;i--) #define REPO(i, n) for(ll i = 1;i <= n;i++) #define ll long long #define INF (ll)1ll << 60 #define MINF (-1 * INF) #define ALL(n) n.begin(),n.end() #define MOD (ll)1000000007 #define P pair int main(){ int n; cin >> n; vector s(n), v; REP(i, n)cin >> s[i]; REP(i, n){ FOR(j, i + 1, n){ v.push_back(s[i] + s[j]); v.push_back(s[j] + s[i]); } } sort(ALL(v)); v.erase(unique(ALL(v)), v.end()); cout << v.size() << endl; }