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 Ruby (2.7.1) (judge verdict: Accepted)

N=gets.to_i
S=gets.chomp

s=S.split("").select {|x|x=="#"}.length
d=N-s

l=[0,0]
r=[s,d]

ret = N
(0..N).each do |i|
    rr = l[0] + r[1]
    ret = rr if rr < ret
    if S[i] == "#"
        r[0]-=1
        l[0]+=1
    else
        r[1]-=1
        l[1]+=1
    end
end
puts ret