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)

process.stdin.resume();
process.stdin.setEncoding('utf8'); 
var lines = [];
var reader = require('readline').createInterface({
	input: process.stdin,
	output: process.stdout
});
 
reader.on('line', (line) => {
	lines.push(line);
});

reader.on('close', () => {
	"use strict"
	const N = +lines[0];
	const S = lines[1];
	
	const nB = S.match(/#/g) ? S.match(/#/g).length : 0;
	const nW = N - nB;
	
	let ans = nW;
	let bestAns = nW;
	for(let i=0; i<N; i++){
		S[i]=="#" ? ans++ : ans--;
		bestAns>ans && (bestAns=ans);
	}
	
	console.log(bestAns);
});