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)

def minToggle(arr, n): 
  
    zero =[0 for i in range(n + 1+1)] 
    zero[0] = 0
   
    # Fill entries in zero[] 
    # such that zero[i] 
    # stores count of zeroes 
    # to the left of i 
    # (exl 
    for i in range(1, n + 1): 
      
        # If zero found 
        # update zero[] array 
        if (arr[i-1] == 0): 
            zero[i] = zero[i-1] + 1
        else: 
            zero[i] = zero[i-1] 
   
    # Finding the minimum 
    # toggle required from 
    # every index(0 to n-1) 
    ans = n 
    for i in range(1, n + 1): 
        ans = min(ans, i - zero[i] + zero[n] - zero[i]) 
   
    return ans 
      
# Driver Program 
n=int(input())
s=input().rstrip()
arr=[]
for i in s:
    if i=='.':
        arr.append(0)
    else:
        arr.append(1)
n = len(arr) 
  
print(minToggle(arr, n)) 
  
# This code is contributed 
# by Anant Agarwal.