sample = 10 10 rho "..@@.@@@@.@@@.@.@.@@@@@@@.@.@@@.@@@@..@.@@.@@@@.@@.@@@@@@@.@.@.@.@.@@@@.@@@.@@@@.@@@@@@@@.@.@.@@@.@."

op ch pad g =
    (g, (((rho g)[2]) rho ch)) ,% ((1 + (rho g)[1]) rho ch)

op adj g =
    (1 rot g) + (-1 rot g) + (1 flip g) + (-1 flip g) + (1 rot 1 flip g) + (-1 rot 1 flip g) + (1 rot -1 flip g) + (-1 rot -1 flip g)

op solve g =
    gx = 0 pad (g=="@")
    fx = gx and 4 > adj gx
    +/ ,fx

op remove g =
    next = g - (g and 4 > adj g)
    and/, g == next: g
    remove next

op solve2 g =
    gx = 0 pad (g=="@")
    rx = remove gx
    +/,(gx - rx)

x = "@" == "." pad sample
x
adj x
""
x and 4 > adj x

solve sample
solve2 sample

) get "input.ivy"

solve input
solve2 input