/**
    O(n^2) solution
**/
#include<bits/stdc++.h>
#define maxN 9005
#define MaxVal 7005
using namespace std;
int ap[2*MaxVal],v[maxN],n;
long long sol;
int main()
{
    freopen("medie.in","r",stdin);
    freopen("medie.out","w",stdout);
    scanf("%d",&n);
    for(int i=1;i<=n;i++)
        scanf("%d",&v[i]);
    sort(v+1,v+n+1);
    for(int i=2;i<=n;i++)
        for(int j=i+1;j<=n;j++)
            if((v[i]+v[j])==2*v[1]) sol+=1LL;
    for(int i=1;i<=n;i++)
    {
        sol=sol+1LL*ap[2*v[i]];
        for(int j=i+2;j<=n;j++)
            ap[v[i]+v[j]]++;
        for(int j=1;j<i;j++)
            ap[v[i+1]+v[j]]--;
    }
    printf("%lld\n",sol);
    return 0;
}