#include <bits/stdc++.h>
using namespace std;
 
unordered_map<int,int>mpp;
 
int solve(vector<int>& a){
	int n = a.size();
 
	for(int i=3;i<n;i++){
		mpp[a[i]]++;
	}
 
	int ans = 0;
	for(int i=0;i<n-3;i++){
		for(int j=i+1;j<n-2;j++){
			int k=j+1;
			for(;k<n-1;k++){
				int sum = -(a[i]+a[j]+a[k]);
				ans += mpp[sum];
				mpp[a[k+1]]--;
			}
			for(int z=k+2;z<n;z++){
				mpp[a[z]]++;
			}
		}
	}
	return ans;
}
 
int main() {
	int n;
	cin>>n;
	vector<int>a(n);
	for(int i=0;i<n;i++){
		cin>>a[i];
	}
	cout<<solve(a);
	return 0;
}

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