#include <cstdio>
#include <cstring>

#define MAXN 9005
#define MAXV 7005

int main(){

  freopen("medie.in", "r", stdin);
  freopen("medie.out", "w", stdout);

  int N, i, j, k, cnt;
  int S[MAXN], F[MAXV*2];

  memset(F, 0, sizeof(F));

  scanf("%d", &N);
  for(i=1; i<=N; i++)
    scanf("%d", S+i);

  for(i=2; i<=N; i++)
    for(j=i+1; j<=N; j++)
      F[S[i]+S[j]]++;

  cnt=0;
  for(i=1; i<=N; i++){
    cnt+=F[S[i]*2];
    for(j=i+1; j<=N; j++)
      F[S[i]+S[j]]++;
    for(j=i+2; j<=N; j++)
      F[S[i+1]+S[j]]--;
  }

  printf("%d\n", cnt);

  return 0;

}