#include <iostream>
#include<bits/stdc++.h>
 
using namespace std;
 
 
 
int main() {
	// your code goes here
	int n;
	cin>>n;
	vector<int> arr(n);
	unordered_map<int,int> mpp;
 
	for(int i=0;i<n;i++){
		cin>>arr[i];
	}
 
	for(int i=2;i<n-1;i++){
		for(int j=i+1;j<n;j++){
			int sum = arr[i]+arr[j];
			mpp[sum]++;
		}
	}
	int ans=0;
 
 
	for(int j=1;j<n-2;j++){
		for(int i=0;i<j;i++){
			int target = -(arr[i]+arr[j]);
			if(mpp.find(target)!=mpp.end()){
				ans = ans + mpp[target];
			}
		}
 
		for(int z = j+2;z<n;z++){
			mpp[arr[j+1]+arr[z]]--;
		}
 
	}
 
	cout<<ans<<endl;
 
	return 0;
}

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