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())
tip = []
cnt = 1
s = list(input())
ans = [s.count("#"), s.count(".")]
for i in range(1, n):
    if s[i] == s[i-1]:
        cnt += 1
    else:
        tip.append([s[i-1], cnt])
        cnt = 1
tip.append([s[-1], cnt])


if tip[-1][0] == "#":
    tmp = 0
    for i in range(len(tip) - 1):
        if tip[i][0] == "#":
            tmp += tip[i][1]
    ans.append(tmp)
print(min(ans))