#include <bits/stdc++.h>
using namespace std;
int solution[1000010] = {0};
int main() {
  ios::sync_with_stdio(0);
  int n;
  long long int sum = 0;
  long long int part;
  long long partSum = 0;
  long long int result = 0;
  cin >> n;
  int* a = new int[n];
  for (int i = 0; i < n; ++i) {
    cin >> a[i];
    sum += a[i];
  }
  if (sum % 3)
    cout << "0";
  else {
    part = sum / 3;
    for (int i = 0; i < n; ++i) {
      partSum += a[i];
      if (partSum == part) solution[i] = 1;
    }
    for (int i = 0; i < n - 2; i++) solution[i + 1] += solution[i];
    partSum = 0;
    for (int i = n - 1; i - 2 >= 0; --i) {
      partSum += a[i];
      if (partSum == part) result += solution[i - 2];
    }
    cout << result;
  }
  return 0;
}
