#include <algorithm>
#include <cmath>
#include <functional>
#include <iomanip>
#include <iostream>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <tuple>
#include <vector>
using namespace std;
using ll = int64_t;
#define rep(i, j, n) for (int i = j; i < (n); ++i)
#define rrep(i, j, n) for (int i = (n)-1; j <= i; --i)

int main() {
  int n;
  cin >> n;
  vector<ll> a(n);
  rep(i, 0, n) cin >> a[i];
  sort(a.begin(), a.end());
  // 重複は一個前
  unordered_map<ll, ll> dp;
  rep(i, 0, n) {
    ++dp[a[i]];
    dp[a[i] + 1] += dp[a[i] - 1];
  }
  ll ans = 0;
  for (auto itr : dp) ans += itr.second;
  cout << ans << endl;
  return 0;
}