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)

from __future__ import print_function
import sys

def eprint(*args, **kwargs):
    print(*args, file=sys.stderr, **kwargs)


n=int(input())
S=list(input())

cnt_temp=0
cnt_temp2=0
stack=[]
cnt=0

# # eprint(n)
# # eprint(S)

# for i in range(n):
#     # eprint(i)


flag=0
flag2=0
start=0

for i in range(n):
    if S[i] == '.':
        cnt_temp+=1



if S[0] == '.':
    flag =1
# eprint("flag: ",end="")
# eprint(flag)

if flag==1:
    cnt_temp=0
    for i in range(n-1):
        if S[i]=='#' and S[i+1]=='.':
            flag2=1
            for j in range(i+1,n):
                if S[j] =='.':
                    cnt_temp+=1
            break
# eprint("flag2: ",end="")
# eprint(flag2)
        

        
for _ in S:
    print( _ , end="")
print()
        
for i in range(n-1):
    if S[i]=='#' and S[i+1]=='#':
        stack.append(i)
    elif S[i]=='#' and S[i+1]=='.':
        
        S[i]='.'
        cnt+=1
        
        # for _ in S:
            # eprint(_,end="")
        # eprint()
        
        
        
        while stack!=[]:
            temp=stack.pop()
            S[temp]='.'
            cnt+=1
            # for _ in S:
                # eprint(_,end="")
            # eprint()

            
        
# eprint("cnt: ",end="")
# eprint(cnt)
# eprint("cnt_temp2: ",end="")
# eprint(cnt_temp2)

print(min(cnt,cnt_temp))
            #
    #
    #
    #
    #
    #
    #
    #
    #
    #
    #
    #
    #
    #
    #
    #