#include <bits/stdc++.h>
using namespace std;
#ifdef LOCAL
  #include "settings/debug.cpp"
#else
  #define Debug(...) void(0)
#endif
#define rep(i, n) for (int i = 0; i < (n); ++i)
using ll = long long;
using ull = unsigned long long;

int main() {
  cin.tie(nullptr)->sync_with_stdio(false);
  int n;
  cin >> n;
  vector<int> a(n);
  rep(i, n) cin >> a[i];
  vector<pair<int, int>> b;
  int l = 0;
  while (l < n) {
    int r = l + 1;
    while (r < n && a[r] - a[r - 1] == 1) ++r;
    if (r - l >= 2) b.push_back({ l, r });
    l = r;
  }
  ll ans = 0;
  for (auto [l, r] : b) {
    int m = r - l;
    ans += 1LL * m * (m - 1) / 2;
  }
  cout << ans << '\n';
  return 0;
}