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 (3.8.2) (judge verdict: Accepted)

import sys

n=int(input())
c=input()
black=c.count("#")
white=c.count(".")

if black==n:
  print(0)
  sys.exit()

b=0
w=0
now=0
ans=float('inf')

for i in range(n):
  if c[i]=="#":
    b+=1
  w=(i+1)-b

  now=b+(white-w)
  ans=min(ans,now)
  
print(min(ans,white))