N = int(input())
S = str(input())

white = 0
black = 0

if N != 0:
  if S[N-1] == "#":
    N = N-1

  if S[0] ==".":
    N = N-1

  for i in range(N):
    if S[i] == "#":
      black +=1
    else:
      white +=1
  print(min(white,black))
else:
  print(0)