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 (1.3.71) (judge verdict: Accepted)

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

    val wCnt = IntArray(n) {0}
    val bCnt = IntArray(n) {0}

    wCnt[0] = if (ss[0] == '.') 1 else 0
    bCnt[0] = if (ss[0] == '#') 1 else 0

    for (i in 1 until n) {
        wCnt[i] = wCnt[i-1] + if (ss[i] == '.') 1 else 0
        bCnt[i] = bCnt[i-1] + if (ss[i] == '#') 1 else 0
    }

    var min = wCnt.last()

    for (i in ss.indices) {
        val lMin = bCnt[i]
        val rMin = wCnt.last() - wCnt[i]
        min = Math.min(min, lMin+rMin)
    }

    println(min)
}