Hexadecimal to Decimal Converter

function hexToDec(num)
     if type(num)=="number" then
         error("String expected, got number.", 1)
     end
     local K=string.len(num)
     local N=K-1
     local Z
     local chars={}
     for n in num:gmatch("[%w+]") do
         table.insert(chars, n)
     end
     for key,v in ipairs(chars) do
         if v=="A" then
             chars[key]=tonumber(10)
         elseif v=="B" then
             chars[key]=tonumber(11)
         elseif v=="C" then
             chars[key]=tonumber(12)
         elseif v=="D" then
             chars[key]=tonumber(13)
         elseif v=="E" then
             chars[key]=tonumber(14)
         elseif v=="F" then
             chars[key]=tonumber(15)
         end
     end
     if K==4 then
         Z=(chars[1]*16^N)+(chars[2]*16^N-1)+(chars[3]*16^N-2)+chars[4]
     elseif K==3 then
         Z=(chars[1]*16^N)+(chars[2]*16^N-1)+chars[3]
     elseif K==2 then
         Z=(chars[1]*16^N)+chars[2]
     elseif K>4 then
         error("attempt to convert more than four numbers", 1)
     elseif K<2 then
         error("attempt to convert one number", 1)
     end
     return Z
end

print(hexToDec("5CE"))