Problem:
Score : 300 points

Problem Statement

There are N stones arranged in a row. Every stone is painted white or black.
A string S represents the color of the stones. The i-th stone from the left is white if the i-th character of S is ., and the stone is black if the character is #.

Takahashi wants to change the colors of some stones to black or white so that there will be no white stone immediately to the right of a black stone.
Find the minimum number of stones that needs to be recolored.

Constraints

1 \leq N \leq 2\times 10^5

S is a string of length N consisting of . and #.

Input

Input is given from Standard Input in the following format:

N
S

Output

Print the minimum number of stones that needs to be recolored.

Sample Input 1

3
#.#

Sample Output 1

1

It is enough to change the color of the first stone to white.

Sample Input 2

5
#.##.

Sample Output 2

2

Sample Input 3

9
.........

Sample Output 3

0

Solution in Python (3.4.3) (judge verdict: Wrong Answer)

import sys
def p(*a):
  s=" ".join(map(str,a))
  #print(s)
  sys.stderr.write(s+"\n")


N=int(input())
S=input()
N=len(S)

if (S.count('.')==N) or (S.count('#')==N):
	print(0)
	exit()


#	s = "abc345abc"
#	print(s.find("a"))		#=> 0

i = S.find('#.')
a = S[(i+1):]
b = S[:(i+1)]

p(i, a)
p(i, b)

ans = min(a.count('.'), b.count('#'))
print(ans)


#		l = sorted(s, reverse=True)
#		print(l)						#=> ['y', 't', 'o', 'n', 'h', 'P']
#		print( "".join(l) )				#=> ytonhP