#include <stdio.h>
#include <atcoder/all>
#include <bits/stdc++.h>
using namespace std;
using namespace atcoder;
using mint = modint998244353;
#define rep(i,n) for (int i = 0; i < (n); ++i)
#define Inf32 1000000001
#define Inf64 4000000000000000001



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