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 Kotlin (1.0.0) (judge verdict: Wrong Answer)

fun main(args: Array<String>) {
    val n = readLine()!!.toInt()
    val s = readLine()!!

    var ans = 0

    var b = 0
    var w = 0

    if (s[0] == '#') {
       b++
    }

    for (i in (1 until n)) {
        if (s[i] == '#') {
            b++
        } else {
            w++
        }

        if (i < n - 1 && s[i] == '.' && s[i + 1] == '#') {

            if (b > w) {
                ans += w
                b += w
                w = 0
                continue
            }

            ans += b
            b = 0
            w = 0
        }
    }

    ans += Math.min(b, w)

    println(ans)
}