#include <iostream>
using namespace std;
using ll = long long;

int main()
{
  int n;
  cin >> n;
  bool exist[200010] = {};
  for (int i = 0; i < n; i++)
  {
    int a;
    cin >> a;
    exist[a] = true;
  }
  ll dp[200010] = {};
  dp[1] = exist[1], dp[2] = exist[2];
  for (int i = 3; i < 200005; i++)
  {
    dp[i] += exist[i];
    if (exist[i - 1])
      dp[i] += dp[i - 2];
  }
  ll sum = 0;
  for (int i = 1; i < 200010; i++)
    sum += dp[i];
  cout << sum << endl;
  return 0;
}