Find the average curve of multiple plots from different Excel files

I have multiple excel files each having 2 columns, all numerical values. I have managed to make a plot which has all the lines superimposed, without actually extracting separate variables in the workspace. But now I need to find a line that is an average of all the other lines, and I can't figure it out. Might be more difficult since I don't have the variables extracted. This is the code. Thank you in advance!

Files = dir('E:\...');
N = length(Files);

for i = 3:N  
    m = sprintf('%s', Files(i,1).name);
    Frequency = xlsread(m,'A:A');
    Density = xlsread(m,'B:B'); 
    plot(Density,Frequency)
    hold on
    xlabel('Density')
    ylabel('Frequency')
    xlim([0 1.4]);
    ylim([0 7000]);
end

Answer 1

[Sruthi Geetha]

You can find the sum of the frequency and density values for each file and then divide by N to get the mean of frequency and density respectively. Then plot them. It would look something like this:|

endFiles = dir('E:\...');
  N = length(Files);
f = 0;
d = 0;
  for i = 3:N  
      m = sprintf('%s', Files(i,1).name);
      Frequency = xlsread(m,'A:A');
      Density = xlsread(m,'B:B'); 
f = f + xlsread(m,'A:A');
d = d + xlsread(m,'B:B');
      plot(Density,Frequency)
      hold on
      xlabel('Density')
      ylabel('Frequency')
      xlim([0 1.4]);
      ylim([0 7000]);
  end
fmean = f/N;
dmean = d/N;
plot(fmean,dmean);
hold off

[Carla Baceanu]

Thank you, I follow the logic! How can I fix the problem if the number of rows are different? Files have different matrix sizes, and there is an error "matrix dimensions must agree"

f = f + xlsread(m,'A:A');
d = d + xlsread(m,'B:B');