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 JavaScript (node.js v5.12) (judge verdict: Wrong Answer)

function main(input) {
  const s = [].slice.call(input.split(/\n/)[1]) 
  var c = 0
  
  for (var i=0; i<s.length; i++) {
    if (s[i] === ".") {
      if (i - 1 < 0) {
        continue
      }
      
      if (s[i-1] === "#") {
        c++
        s[i] = "#"
        
        for (var j=i-2; j>=0; j--) {
          if (s[j] === ".") { break }
          
          c++
          s[j] = "#"
        }
      }
    } else {
      if (s.length - i < 2) {
        continue
      }
      
      if (s[i+1] === "." && s[i+2] === ".") {
        c++
        s[i] = "."
        
        for (var j=i-1; j>=0; j--) {
          if (s[j] === ".") { break }
          
          c++
          s[j] = "."
        }
      }
    }
      
  }
  
  console.log(c)
}

main(require("fs").readFileSync("/dev/stdin", "utf8"));