N, M = gets.split.map(&:to_i)
D = M.times.map {gets.to_i}
L = D.select {|d| d < 0}.map(&:abs).sort
R = D.select {|d| d >= 0}.sort
ans = ([0, N - L.size].max..[N, R.size].min).map {|k|
  x = [0, *R[0, k]].max
  y = [0, *L[0, N - k]].max
  (x == 0 || y == 0) ? [x, y].max : 2*[x, y].min + [x, y].max}.min
puts ans