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)

import java.lang.Math.min

fun Boolean.toInt() = if (this) 1 else 0

fun main(args: Array<String>) {
    val n = readLine()!!.toInt()
    val s = readLine()!!.reversed()
    var dp = Array(2) {
        Array<Int>(n + 1) { 0 }
    }
    for (i in listOf(0, 1)) {
        for (j in 0 until n) {
            dp[0][j + 1] = dp[0][j] + (s[j] == '.').toInt()
            dp[1][j + 1] = min(dp[0][j], dp[1][j] + (s[j] == '#').toInt())
        }
    }
    println(min(dp[0][n], dp[1][n]))
}