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())

ans = 0
T1 = S.copy()
f = False
for i in range(N):
    s = T1[i]
    if s == ".":
        continue
    else:
        if i < N - 1 and T1[i+1] == ".":
            if not f and i + 1 < N - 1 and T1[i+2] == ".":
                ans += 1
            else:
                f = True
                T1[i+1] = "#"
                ans += 1
        else:
            f = True
ans2 = 0

for i in range(N):
    s = S[i]
    if s == ".":
        continue
    else:
        ans2 += 1

ans3 = 0

for i in range(N):
    s = S[i]
    if s == ".":
        ans3 += 1
    else:
        continue

while S[-1] != ".":
    S.pop()
N = len(S)
ans4 = 0
for i in range(N):
    s = S[i]
    if s == ".":
        continue
    else:
        ans4 += 1

# print(ans, ans2, ans3)
print(min(ans2, ans, ans3, ans4))