print("Press any key in 3 seconds to skip startup...")
local timer = os.startTimer(3)
while true do
     local e = {os.pullEvent()}
     if e[1] == "key" then
         print("Startup skipped.")
         return
     elseif e[1] == "timer" and e[2] == timer then
         break
     end
 end
 
shell.run("program")