Calculate Fibonacci number

#include <iostream>
using namespace std;

// Generate any fibonacci number
// from the 1st to the 47th
// The data type unsigned is 4 bytes.
int main()
{
    unsigned which_fibonacci = 0; // Which number to show.
    unsigned first = 0; // First number in the sum.
    unsigned second = 1; // Second number in the sum.
    unsigned next = 1; // Current sum (fibonacci number).
    unsigned final_fibonacci = 0; // Result.

    cout << "Which fibonacci number would you like to see? (1 - 47)\n";
    cin >> which_fibonacci; // Get user request.
    // Only numbers in position 1 to 47 can be displayed with 4 bytes.
    // If the user request is outside that range,
    while ( (which_fibonacci < 1) || (which_fibonacci > 47) )
    {
        cout << "Please choose a number from 1 to 47\n";
        cin >> which_fibonacci; // Get new request.
    }

    // If the first or second fibonacci number is requested,
    if (which_fibonacci == 1 || which_fibonacci == 2)
    {
        final_fibonacci = 1; // It is 1.
    }
    else // If the third or greater fibonacci number is requested,
    {
        // Do the computation the proper number of times.
        for (int i = 1; i <= (which_fibonacci - 2); ++i)
        {
            // Shift the addition to the last two
            // fibonacci numbers.
            first = second;
            second = next;
            next = first + second; // Calculate the next number.
        }

        final_fibonacci = next; // This is the result.
    }

    cout << "Fibonacci number " << which_fibonacci << " is " << final_fibonacci << '\n';

    // End the program.
    return 0;
}