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=str(input())

def count_renzoku(S,s):
    renzoku=1
    for i in range(1,len(S)):
        if S[i]==s:
            renzoku+=1
        else:
            break
    return renzoku

if S.count('#')==N or S.count('.')==N:
    print(0)
else:
    a=min(S.count('#'),S.count('.'))
    T=S[::-1]
    if T[0]=='#':
        T=T[count_renzoku(T,'#'):]
        U=T[::-1]
        if U[0]=='.':
            U=U[count_renzoku(U,'.'):]
        b=min(U.count('#'),U.count('.'))
        print(min(a,b))
    elif S[0]=='.':
        S=S[count_renzoku(S,'.'):]
        b=min(S.count('#'),S.count('.'))
        print(min(a,b))
    else:
        print(a)