// RANKDIR: TB
rank of "0"  is 1
rank of "1"  is 1
rank of "2"  is 1
rank of "3"  is 1
rank of "4"  is 1
rank of "5"  is 1
rank of "6"  is 1
rank of "8"  is 1
rank of "15"  is 1
rank of "18"  is 1
rank of "10"  is 2
rank of "16"  is 2
rank of "17"  is 2
rank of "20"  is 2
rank of "12"  is 2
rank of "14"  is 2
rank of "19"  is 2
rank of "9"  is 2
rank of "13"  is 2
rank of "7"  is 2
rank of "11"  is 2
