#include <bits/stdc++.h>
using namespace std;

int n, a;
long long m;
map<int, long long> Mp;

int main() {
	cin >> n;

	for (int i = 0; i < n; i++) {
		cin >> a;

		if (Mp.find(a - 1) == Mp.end()) {
			Mp[a] = 0;
		}
		else {
			Mp[a] = Mp[a - 1] + 1;
			m += Mp[a];
		}
	}

	cout << m << endl;
}