d = gets.to_i
x = "x"*14
ma = -1
s = x + gets.chomp + gets.chomp + x
(0...42).each do |i|
  _s = s.dup
  _s[i..-1] =~ Regexp.new("^(x{0,#{d}})")
  l = $1.length
  _s[i...(i+l)] = "o"*l
  ma = [ma, (_s.split("x").sort[-1]||"").length].max
end
p ma