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: Accepted)

fun main(args: Array<String>) {
    val N = readLine()!!.toInt(); val S = readLine()!!

    val W = S.split("#").filter { it.isNotBlank() }.map { it.length }.let { if (S.first() == '.') it.drop(1) else it }
    val B = S.split(".").filter { it.isNotBlank() }.map { it.length }

    val sw = mutableListOf<Int>()
    sw.add(W.sum())
    W.forEach { sw.add(sw.last() - it) }

    val sb = mutableListOf<Int>()
    sb.add(0)
    B.forEach { sb.add(sb.last() + it) }

    val counts = mutableListOf<Int>()
    counts.add(sb.last())
    for (i in B.indices) {
        val w = if (i in sw.indices) sw[i] else 0
        val b = if (i in sb.indices) sb[i] else 0
        counts.add(w + b)
    }
    println(counts.min())
}