#include <stdio.h>

#define MAX_VAL 7005
#define FIN "medie.in"
#define FOUT "medie.out"

int N, cnt[MAX_VAL];
long long Res;

int main(void)
{
    int i, j, n;

    freopen(FIN, "r", stdin);
    freopen(FOUT, "w", stdout);

    scanf("%d", &N);
    for (i = 0; i < N; ++i)
    {
        scanf("%d", &n);
        ++cnt[n];
    }

    for (i = 0; i < MAX_VAL; ++i)
    {
        if (!cnt[i]) continue;
        for (j = i+2; j < MAX_VAL; j += 2)
            Res += cnt[(i+j)>>1]*cnt[i]*cnt[j];
    }

    for (i = 0; i < MAX_VAL; ++i)
        Res += cnt[i]*(cnt[i]-1)*(cnt[i]-2)/2;

    printf("%lld\n", Res);

    return 0;
}