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: Accepted)

function MainC(input) {
	input = input.split("\n");
	var n = input[0];
	var s = input[1];
	var result = 0;
  
  var whiteStones = 0;
	for(var i = 0; i < n; i++){
		if(s[i] == "."){
			whiteStones += 1;
		}
	}
    
  var changeStones = whiteStones;
	var minChange = changeStones;
	for(var i = 0; i < n; i++){
		if(s[i] == "#"){
			changeStones += 1;
		}else{
			changeStones -= 1;
		}
		if(minChange > changeStones) minChange = changeStones;		
	}
	console.log('%d',minChange);
}
//*この行以降は編集しないでください（標準入出力から一度に読み込み、Mainを呼び出します）
MainC(require("fs").readFileSync("/dev/stdin", "utf8"));