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)

l = int(input())
ss = input()
bits = ''.join(list(map(lambda s: '0' if s == '.' else '1', ss)))
n0 = bits.find('0')
n1 = bits.find('1')
if 0 <= n1:
    sbits = (''.join('0' for _ in range(n1))).join('1' for _ in range(l-n1))
    c0 = bin(int(bits, 2) ^ int(sbits,2)).count('1')
    sbits = (''.join('0' for _ in range(n0))).join('1' for _ in range(l-n0))
    c1 = bin(int(bits, 2) ^ int(sbits,2)).count('1')
    print(c0 if c0 < c1 else c1)
else:
    print(0)