#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
const ll N=1e5+1e4;
ll n,a[N],b[N],ans,maxn;
signed main()
{
    cin>>n;
    for(ll i=1;i<=n;i++)
    {
        cin>>a[i];
        b[a[i]]++;
        maxn=max(maxn,a[i]);
    }
    for(ll i=0;i<=maxn;i++)
    {
        ans+=(b[i]*b[i+1]);//若值为i的数有b[i]个，值为i+1的数有b[i+1]，则ans+=（b[i]*b[i+1]）(组合)
    }
    cout<<ans;
}