class SegTree
  attr_reader :size, :e, :f
  attr_accessor :seg

  def self.create(a=[],e,f)
    n = 1
    n *= 2 while n < a.size
    this = new(n,e,f)
    a.size.times do |i|
      this.seg[i+n] = a[i]
    end
    (n-1).downto(1) do |i|
      this.seg[i] = f[ this.seg[i*2],this.seg[i*2+1] ]
    end
    this
  end

  def initialize(n=2**32,e,f)
    @size = n
    @e = e
    @f = f
    @seg = Array.new(size*2, e)
  end

  def [](i)
    i += size
    seg[i]
  end

  def update(i,x)
    i += size
    seg[i] = x
    while i > 1
      i /= 2
      seg[i] = f[ seg[i*2], seg[i*2+1] ]
    end
  end

  def query(a,b)
    ans = e
    a += size; b += size
    while a < b
      (ans = f[ ans, seg[a] ]; a += 1) if a.odd?
      (b -= 1; ans = f[ ans, seg[b] ]) if b.odd?
      a /= 2; b /= 2
    end
    ans
  end

  def inspect
    { size: size, seg: seg }.to_s
  end
end

# SegTree.new(N,E,F) := 要素数N、単位元E、演算Fで初期化、ただしNは2の冪
# SegTree.create(A,E,F) := モノイドA、単位元E、演算Fで初期化で初期化
# update(i,x) := A[i]をxに更新
# query(a,b) := 半開区間[a,b)でのA[i]の演算結果
#
# 単位元を追加してモノイドにする例（gcd）
# E = -1
# F = -> x,y { x == E ? y : y == E ? x : x.gcd(y) }
# T = SegTree.create(a,E,F)

n = gets.to_i
Black = gets.chomp.chars.map{|c| c == "#" ? 1 : 0 }
White = Black.map{|i| 1 - i }

E = 0
F = -> x,y { x + y }
BlackTree = SegTree.create(Black,E,F)
WhiteTree = SegTree.create(White,E,F)

ans = 10**6
0.upto(n) do |i|
  num = BlackTree.query(0,i) + WhiteTree.query(i,n)
  ans = num if ans > num
end

puts ans
