function output_sum = task_two(start_element_value, end_element_index, constant)
%% HOW TO
%     start_element_value - first a element
%     end_element_index - n (how many values of elements we should calculate)
%     constans - m constans added to each elemect according to formula:
%     a(n)=a(n-1)+m
%     output - vector with calculeted elements
%     element - current callculeted element 
%% MAIN CODE
    
    % Initializaiton of default values for arguments
    default_a1 = 1;
    default_n = 10;
    default_m = 1;
    
    if nargin == 0 % If a1, n, m is missing set default values for a1, n, m.        
        %error('Please provide a1 value'); <- uncomment if a1 is mandatory
        % and comment three lines below
        start_element_value = default_a1;
        end_element_index = default_n;
        constant = default_m;
    end
    if nargin == 1 % If n and m is missing set default values for n and m.
        end_element_index = default_n;
        constant = default_m;
    end
    if nargin == 2 % If m is missing set default value for m.
        constant = default_m;
    end
    if nargin > 3 % If 4 or more argumentrs provided skip input parssing
        error('To many arguments to parse')
    end
    
    output(1,1) = start_element_value ;
    element =  output(1,1); % Initialization of a1
    for step=2:1:end_element_index % calculations starts for a2 element
        element = element + constant; % a(n) = a(n-1) + m
        output(1, step) = element; % append calculated value on an index
    end
    output_sum = sum(output);
end