Derangement Number By Dynamic Programming

#include<bits/stdc++.h>
#define ll long long int
using namespace std;

ll counter(int n)
{
    ll d[n+1], i;

    d[0] = 1;
    d[1] = 0;
    d[2] = 1;

    for(i=3;i<=n;i++)
    {
        d[i] = (i-1) * (d[i-1] + d[i-2]);
    }

    return d[n];
}

int main()
{
    int n;

    cout << "Enter A Number :: ";
    cin >> n;

    ll Derangement_Number = counter(n);

    cout << "\n" << n << " Element Derangement Number is :: " << Derangement_Number << "\n";

    return 0;
}