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 PyPy3 (2.4.0) (judge verdict: Accepted)

n=int(input())
s=input()
sb=[0]*n
sw=[0]*n
wb=[]
for i in range(n-1):
    if s[i:i+2]==".#":
        wb.append(i)
for i in range(n):
    if s[i]==".":
        if i==0:
            sw[i]=1
        else:
            sw[i]=1+sw[i-1]
            sb[i]=sb[i-1]
    else:
        if i==0:
            sb[i]=1
        else:
            sb[i]=1+sb[i-1]
            sw[i]=sw[i-1]
anses=[len([x for x in s if x=="#"]),len([x for x in s if x=="."])]
for i in wb:
    anses.append(sb[i]+sw[n-1]-sw[i])
print(min(anses))