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 Fortran (gfortran v4.8.4) (judge verdict: Accepted)

program tenka1_2019_c
    use,intrinsic :: iso_fortran_env
    implicit none
    integer(int32):: n,i,cl,cr,ans
    character(:),allocatable:: s

    read*, n
    allocate(character(n):: s)
    read*, s(:)
    cl = 0
    cr = 0
    do i=1,n
        if (s(i:i) == '.') cr=cr+1
    end do

    ans = cl+cr

    do i=1,n
        if (s(i:i) == '.') then
            cr=cr-1
        else
            cl=cl+1
        end if
        ans = min(ans,cl+cr)
    end do

    print'(i0)', ans
end program tenka1_2019_c