#include<bits/stdc++.h>
using namespace std;
#define int long long
#define REP(i,m,n) for(int i=(m);i<(n);i++)
#define rep(i,n) REP(i,0,n)
#define pb push_back
#define all(a) a.begin(),a.end()
#define rall(c) (c).rbegin(),(c).rend()
#define mp make_pair
#define endl '\n'
#define vec vector<ll>
#define mat vector<vector<ll> >
#define fi first
#define se second
typedef long long ll;
typedef unsigned long long ull;
typedef pair<ll,ll> pll;
typedef long double ld;
typedef complex<double> comp;
const ll INF=1e9+7;
const ll inf=INF*INF;
const ll MOD=1e9+7;
const ll mod=MOD;
const int MAX=200010;



signed main(){
    ll n;cin>>n;
    vector<ll>a(n);
    rep(i,n)cin>>a[i];
    map<ll,ll>ma;
    sort(all(a));
    rep(i,n){
        ma[a[i]]++;
        ma[a[i]+1]+=0;
    }
    ll ans=0;
    for(auto e:ma){
        if(ma.find(e.fi-1)!=ma.end())ma[e.fi]+=ma[e.fi-2];
        ans+=ma[e.fi];
        //cout<<e.fi<<' '<<ma[e.fi]<<endl;
    }
    cout<<ans<<endl;
}