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 lCumSum = mutableListOf(0)
    for(i in 1..n) {
        lCumSum.add(lCumSum[i - 1] + if(s[i-1] == '#') 1 else 0)
    }

    var minAns = n
    for(i in 0..n) {
        val ans = lCumSum[i] + ((n - i) - (lCumSum[n] - lCumSum[i]))
        minAns = listOf(minAns, ans).min()!!
    }
    println(minAns)
}