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)

"use strict";
    
const main = arg => {
    arg = arg.trim().split("\n");
    const N = ~~arg[0];
    const S = arg[1].split("");
    const rS = [...S].reverse();
    
    let flg1 = false;
    let hasBlack = false;
    let cnt1 = 0;
    
    for(let i=0; i<N; i++) {
        if(S[i] === "#" && !hasBlack) {
            hasBlack = true;
        }
        
        if(hasBlack) {
            if(!flg1 && S[i] === ".") {
                cnt1++;
                flg1 = true;
            } else if(flg1 && S[i] === ".") {
                cnt1++;
            }
        }
    }
    
    let flg2 = false;
    let hasWhite = false;
    let cnt2 = 0;
    
    for(let i=0; i<N; i++) {
        if(rS[i] === "." && !hasWhite) {
            hasWhite = true;
        }
        
        if(hasWhite) {
            if(!flg2 && rS[i] === "#") {
                cnt2++;
                flg2 = true;
            } else if(flg2 && rS[i] === "#") {
                cnt2++;
            }
        }
    }
    
    console.log(Math.min(cnt1, cnt2));
}
main(require('fs').readFileSync('/dev/stdin', 'utf8'));