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: Time Limit Exceeded)

n = int(input())
s = input()

l = []
for i in range(n):
    if i == 0:
        l.append(1)
        continue
    if s[i] == s[i-1]:
        l[-1]+=1
    else:
        l.append(1)

if s[0]=='.':
    l = l[1:]
if s[-1]=='#':
    l = l[:-1]

bw = sum(l[1::2])

for i in range(len(l)//2+1):
    bw = min(bw, sum(l[:2*i+1:2])+sum(l[2*i+1::2]))

print(bw)