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)

N=int(input())
S=input()
tmp=1
L=[]
ans=10**6
black=0
white=0
for i in range(1,len(S)):
    if S[i]==S[i-1]:
        tmp+=1
    else:
        L.append(tmp)
        tmp=1
    if i ==len(S)-1:
        L.append(tmp)

    if S[i]=='#':
        black+=1
    else:
        white+=1
cul=[0]*(len(L)+2)
for i in range(len(L)):
    cul[i+2]=L[i]+cul[i-2]


if S[0]=='.':
    for i in range(2,len(cul)):
        if i%2==0:
            ans=min(ans,cul[i-1]+white-cul[i])
        else:
            ans=min(ans,cul[i]+white-cul[i-1])
else:
    for i in range(2,len(cul)):
        if i % 2 == 0:
            ans = min(ans,cul[i]+white-cul[i-1])
        else:
            ans = min(ans,cul[i-1]+white-cul[i])


if len(L)==1:
    ans=0
else:
    ans=min(ans,sum(L[0::2]),sum(L[1::2]))

print(ans)