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 Go (1.6) (judge verdict: Wrong Answer)

package main
import "fmt"
func main() {
  var n,x,y,lb,rw int
  var s string
  fmt.Scan(&n)
  fmt.Scan(&s)
  for i:=0;i<n;i++ {
    if s[i:i+1] == "." {
      rw++
    }
  }
  x = 2*n
  for i:=0;i<n+1;i++ {
    y = lb+rw
    if i == n { break }
    if x > y { x = y }
    if s[i:i+1] == "." {
      rw--
    } else {
      lb++
    }
  }
  fmt.Println(x)
}