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: Runtime Error)

N=int(input())
S=input()
before=''
count=0
count_list=[]
for i,moji in enumerate(S):
    count+=1
    if moji!=before:
        before=moji
        count_list.append(count)
        count=0
    elif i-1==len(S):
        count_list.append(count)
cand=[]

if S[0]=='.':
    count_list=count_list[1:]
    length=len(count_list)
    if length%2==1:
        ki=1
    for i in range(length-1//2+1):
        cand.append(sum(count_list[0:max_num-i*2:2])+sum(count_list[i*2+1::2]))
else:
    length=len(count_list)
    ki=0
    if length%2==1:
        ki=1
    max_num=length//2
    for i in range(length//2+1):
        cand.append(sum(count_list[0:length-i*2-ki:2])+sum(count_list[length-i*2:length:2]))
        #print(length-i*2-ki)
        #print(count_list[i*2+1::2])
print(min(cand))