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() #all# or all. or あるところから#
m=S.count('.')
b=[0]*(N+1)
a=[0]*(N+1)
m=N
for i in range(N):
  if S[i]=='#':
    b[i+1]=b[i]+1
    a[i+1]=a[i]
  else:
    b[i+1]=b[i]
    a[i+1]=a[i]+1
for j in range(N+1):
  m=min(m,b[j]+(a[N]-a[j]))
print(m)