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=list(input())
dot=0
sha=0
s_r=list(reversed(S))
#print(s_r)
for i in range(N):
    if S[i] == ".":
        dot=i
        #break
for i in range(N):
    if s_r[i] == "#":
        sha=i
        #break

count=0
#print(dot)#左から
#print(sha)#右から
count_a=0
count_b=0

if dot<=sha:
    for i in range(N):
        if i<dot and S[i]!=".":
            count_a+=1
    for i in range(N):
        if i<sha and s_r[i]!="#":
            count_b+=1
    #print(count)
    c=count_a+count_b
else:
    d=min(count_a,count_b)

a=0
b=0

for i in range(N):
    if S[i]!=".":
        a+=1
    if S[i]!="#":
        b+=1

#print(count)
ans=min(a,b,c,d)
print(ans)