--Lua 5.4.2
local File = io.open("input.txt", "r")

if not File then
    print("File not found")
    return
end

local SafeReports = 0

for Line in File:lines() do
    local IsSafe = true
    local LastSign = 0
    local LastNumber
    for Number in Line:gmatch("%d+") do
        if not LastNumber then
            LastNumber = Number
            goto continue
        end
        local Difference = math.abs(Number - LastNumber)
        if Difference > 3 or Difference == 0 then
            IsSafe = false
            break
        end
        local Sign = (Number - LastNumber) > 0 and 1 or -1
        if LastSign == 0 then
            LastSign = Sign
        else
            if Sign ~= LastSign then
                IsSafe = false
                break
            end
        end
        LastNumber = Number
        ::continue::
    end
    if IsSafe then
        SafeReports = SafeReports + 1
    end
end

print("Safe reports:", SafeReports)