def ascan; gets.split.map(&:to_i); end

N,M,P,Q = ascan

n = N

i = 1
loop do
    n -= M
    n -= M if P-1 <= (i-1)%12 && (i-1)%12 <= P+Q-2
    if n == 0
        p i
        exit
    end
    i += 1
end