A, B, N, M = gets.split.map(&:to_i)
puts (0 .. 10**19).bsearch { |c|
    next false if [A, B].max < c
    x = A - c
    y = B - c
    if x < 0
        if y < 0
            false
        else
            -x <= y / M
        end
    else
        if y < 0
            -y <= x / N
        else
            true
        end
    end
}