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) {
  // 数字
  var N = parseInt(input[0], 10);
  var S = input[1];
  // 文字
  // var A = input[0];

  var result = 0;
  var continueWhite = false;
  var blackNum = S.charAt(0) === '#' ? 1 : 0;

  for (var i = 1; i < S.length; i++) {
    if (S.charAt(i) === '.') {
      if (S.charAt(i - 1) === '#' || continueWhite) {
        result++;
        continueWhite = true;
      }
    } else {
      if (i !== S.length - 1) {
        blackNum++;
      }
      continueWhite = false;
    }
  }
  console.log(result < blackNum ? result : blackNum);
}

Main(require("fs").readFileSync("/dev/stdin", "utf8").trim().split(/\n|\s/));