#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
#define ll long long
#define rep(i, n) for (int i = 0; i < (n); i++)
#define coutf(f) cout << fixed << setprecision(f)
#define all(v) (v).begin(), (v).end()
#define rall(v) (v).rbegin(), (v).rend()

int main() {
	int n;
	cin >> n;
	vector<int> a(n);
	rep(i, n) cin >> a[i];
	vector<ll> c;
	rep(i, n) {
		if (c.size() != 0 && a[i] == a[i - 1] + 1) c.back()++;
		else c.push_back(1);
	}
	ll ans = 0;
	rep(i, c.size()) ans += c[i] * (c[i] + 1) / 2;
	ans -= n;
	cout << ans << endl;
	return 0;
}