N,M,P,Q = gets.split.map(&:to_i)

Year = 12*M + Q*M

n = N / Year
remain = N % Year

drop = 0
r = 0
for i in 1..11 do
    drop += M
    if P <= i && i <= (P+Q - 1) then
        drop += M
    end
    if drop > remain then
        break
    end
    r += 1
end

puts n*12 + r