public class OddNumberSum {
    public static void calculateSum() {
        List<Integer> oddNumbers = new List<Integer>(); // List to store odd numbers
        Integer num = 1; // Start from 1
        Integer sum = 0; // Variable to store the sum
        Integer position = 0; // Position index for the list

        // Use a while loop to add odd numbers to the list
        while (num <= 20) {
            if (num % 2 != 0) { // Check if the number is odd
                oddNumbers.add(num);
            }
            num++; // Increment number
        }

        // Debug log to print the list of odd numbers
        System.debug('Odd Numbers List: ' + oddNumbers);

        // Loop through the list and sum only numbers at even positions
        for (Integer i = 0; i < oddNumbers.size(); i++) {
            if (i % 2 != 0) { // Check if index is even-positioned (1-based)
                sum += oddNumbers[i];
            }
        }

        // Print the final sum in the debug log
        System.debug('Sum of numbers at even positions: ' + sum);
    }
}