file = io.open("input")
io.input(file)

score = 0

function find_duplicates(first, second)
    for i = 1, #first do
        local char = string.sub(first, i, i)

        if string.match(second, char) then
            if char == string.upper(char) then
                return string.byte(char) - string.byte("A") + 27
            elseif char == string.lower(char) then
                return string.byte(char) - string.byte("a") + 1
            end
        end
    end
end

for line in file:lines() do
    local first = string.sub(line, 1, #line/2)
    local second = string.sub(line, #line/2 + 1, #line)

    score = score + find_duplicates(first, second)
end

print(score)