#include <cstdio>
#include <cstring>
#include <iostream>
#include <string>
#include <cmath>
#include <bitset>
#include <vector>
#include <map>
#include <set>
#include <queue>
#include <deque>
#include <algorithm>
#include <complex>
#include <unordered_map>
#include <unordered_set>
#include <random>
#include <cassert>
#include <fstream>
#include <utility>
#include <functional>
#include <time.h>
#include <stack>
#include <array>
#define popcount __builtin_popcount
using namespace std;
using ll=long long;
typedef pair<int, int> P;
ll solve(vector<ll> v){
    vector<ll> v1, v0, w0, w1;
    for(auto x:v){
        if(x&1) v1.push_back(x), w1.push_back(x);
        else v0.push_back(x), w0.push_back(x);
    }
    for(int i=0; i<v0.size(); i++) v0[i]-=2*i;
    for(int i=0; i<v1.size(); i++) v1[i]-=2*i;
    ll ans=0;
    for(int i=0; i<v0.size(); i++){
        ll x=w0[i];
        int t=lower_bound(w1.begin(), w1.end(), x+1)-w1.begin();
        if(t==w1.size() || w1[t]>x+1) continue;
        int u=upper_bound(v1.begin(), v1.end(), v1[t])-v1.begin();
        ans+=u-t;
    }
    for(int i=0; i<v1.size(); i++){
        ll x=w1[i];
        int t=lower_bound(w0.begin(), w0.end(), x+1)-w0.begin();
        if(t==w0.size() || w0[t]>x+1) continue;
        int u=upper_bound(v0.begin(), v0.end(), v0[t])-v0.begin();
        ans+=u-t;
    }
    return ans;
}
int main()
{
    int n; cin>>n;
    ll a[200020];
    for(int i=0; i<n; i++){
        cin>>a[i];
    }
    sort(a, a+n);
    vector<ll> v;
    v.push_back(a[0]);
    ll ans=n;
    for(int i=1; i<n; i++){
        if(a[i]-a[i-1]>2){
            ans+=solve(v);
            v.clear();
        }
        v.push_back(a[i]);
    }
    ans+=solve(v);
    cout<<ans<<endl;
    return 0;
}