#include <iostream>
#include <algorithm>
using namespace std;

int a[101];

int main()
{
    int n;
    int cnt = 0, poz, v, mij, ls, ld;
    bool gasit;
    cin >> n;
    for ( int i = 1; i <= n; ++i)
        cin >> a[i];
    sort( a+1, a+1+n);

    for ( int i = 3; i <= n; ++i)
    {
        for ( int j = 1; j <= n; ++j)
        {
            v = a[i] - a[j];
            gasit = false;
            mij = 0;
            ls = j+1;
            ld = i-1;
            while ( !gasit && ls <= ld)
            {
                mij = (ls+ld)/2;
                if ( v == a[mij])
                {
                    poz = mij;
                    gasit = true;
                }
                else
                    if ( v > a[mij])
                    ls = mij+1;
                    else
                        ld = mij-1;
            }
            if ( gasit == true)
                cnt++;
        }
    }
    if ( cnt == 0)
        cout << "NU";
    else
        cout <<cnt;
    return 0;
}