from PIL import Image

fname = input()

image = Image.open(fname)
pix = image.load()

npixels = image.size[0]*image.size[1]
ncloud = 0

for x in range(image.size[0]):
    for y in range(image.size[1]):
        col = pix[x,y]
        if col[0] >= 192 and col[1] >= 192 and col[2] >= 192:
            ncloud += 1

print(ncloud/npixels*100)