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=[]
w_count_list=[0]
b_count_list=[0]
for i,moji in enumerate(S):
    count+=1
    if moji!=before:
        if i!=0:
            count_list.append(count-1)
            if before=='.':
                w_count_list.append(w_count_list[-1]+count-1)
            else:
                b_count_list.append(b_count_list[-1]+count-1)
            count=1 
            before=moji
    if i==len(S)-1:
        count_list.append(count)
        if moji=='.':
            w_count_list.append(w_count_list[-1]+count)
        else:
            b_count_list.append(b_count_list[-1]+count)
cand=[]
ki=0
if S[0]=='.':
    count_list=count_list[1:]
    length=len(count_list)
    if length%2==1:
        ki=1
    for i in range(length//2+1):
        cand.append(w_count_list[-1]-w_count_list[i]+b_count_list[-1]-b_count_list[max_num+ki-i])
else:
    length=len(count_list)
    if length%2==1:
        ki=1
    max_num=length//2
    for i in range(length//2+1):
        cand.append(w_count_list[-1]-w_count_list[i]+b_count_list[-1]-b_count_list[max_num+ki-i])
        #print(length-i*2-ki)
        #print(count_list[i*2+1::2])
print(min(cand))
#print(cand)