#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using pll = pair<ll, ll>;
#define drep(i, cc, n) for (ll i = (cc); i <= (n); ++i)
#define rep(i, n) drep(i, 0, n - 1)
#define all(a) (a).begin(), (a).end()
#define pb push_back
#define fi first
#define se second

const ll MOD = 1000000007;
const ll MOD2 = 998244353;
const ll INF = 1LL << 60;
const ll MAX_N = 2e5;

int main(){
    ll n;
    cin >> n;
    
    vector<ll> a(n);
    rep(i, n) cin >> a[i];

    ll ans = 0;
    for(ll l=0, r=1; l<n; l++){
        if(l == r) r++;
        if(r < n){
            while(a[r-1]+1 == a[r]){
                r++;
                if(r == n) break;
            }
        }

        ans += r-l-1;
    }

    cout << ans << endl;
}