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import os
from PIL import Image

files = os.listdir('.')
files = filter(lambda x: not x.endswith('.py') and not x.startswith('ex_'), files)
sizes = set()
min_size = 600
for file in files:
    im = Image.open(file)
    if im.size[0] > im.size[1]:
       im = im.resize((int(1.0 * im.size[0] / im.size[1] * min_size), min_size))
    else:
       im = im.resize((min_size, int(1.0 * im.size[1] / im.size[0] * min_size)))
    im.save('ex_' + file)
print('Task Done')