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()

S += "q"

L = []
cnt = 0
for i in range(N) :
    cnt += 1
    if S[i] != S[i+1] :
        L.append(cnt)
        cnt = 0

A = []
B = []

for i in range(len(L)) :
    if i % 2 == 0 :
        A.append(L[i])
    else :
        B.append(L[i])

if len(L) == 1 :
    ans = 0
elif len(L) == 2 :
    if S[0] == "#" :
        ans = min(L)
    else :
        ans = 0
elif len(L) == 3 :
    if S[0] == "#" :
        ans = min(L[0],L[1])
    else :
        ans =min(L[2],L[1])
else :
    if S[0] == "#" :
        if len(L) % 2 == 0 :
            a = min(A.pop(-1), B.pop(-1))
            b = min(sum(A),sum(B))
            ans = a+b
        else :
            A.pop(-1)
            a = min(A.pop(-1), B.pop(-1))
            b = min(sum(A),sum(B))
            ans = a+b
    else :
        if len(L) % 2 == 0 :
            B.pop(-1)
            A.pop(0)
            if len(L) == 4 :
                ans = min(A[0],B[0])
            else :
                a = min(A.pop(-1),B.pop(-1))
                b = min(sum(A),sum(B))
                ans = a+b
        else :
            A.pop(0)
            a = min(A.pop(-1),B.pop(-1))
            b = min(sum(A),sum(B))
            ans = a+b
print(ans)