1         2         3
4   0123456789012345678901234567890
3   .............#....#............
2   .......#..............#........
1   ...............................
0   S........................#.....
-1  ...............................
-2  ...............................
-3  ...........................#...
-4  ...............................
-5  ....................TTTTTTTTTTT
-6  ....................TTTTTTTTTTT
-7  ....................TTTTTTTT#TT
-8  ....................TTTTTTTTTTT
-9  ....................TTTTTTTTTTT
-10 ....................TTTTTTTTTTT

T X y
0 0 0     = 0
1 7  +6   = 7
2 13 +5   = 7 + 6
3 18 +4   = 7 + 6 + 5
4 22 +3   = 7 + 6 + 5 + 4
5 25 +2
6 27 +1
7 28 +0