1                 /\
 2                /  \
 3               /    \
 4              /      \
 5             /        \
 6            /          \
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 8          /\ \____       \
 9         /  \____ \       \
10        /       /  \       \
11       /       /    \    ___\
12      /       /      \  / ____
13     /       /        \/ /    \
14    /       / __________/      \
15   /        \ \                 \
16  /          \ \                 \
17 /           / /                  \
18/___________/ /____________________\