how to find the largest object in the coin image?

how to find the largest object in the image below ? the code I wrote below does not work

A = imread('eight.tif');
C=imbinarize(A);
figure,imshow(C)

B=bwareafilt(C,1);
figure,imshow(B)

Answer 1

[Walter Roberson]

A = imread('eight.tif');
C=imbinarize(A, 'adaptive', 'ForegroundPolarity', 'dark');
figure,imshow(C)

B=bwareafilt(~C,1);
figure,imshow(~B)

[betty]

Thank you very much