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)

inp = require('fs').readFileSync('/dev/stdin', 'utf8').trim().split('\n')
N = inp.shift() * 1
s = inp.shift()
wc = 0
bc = 0
b = [0]
w = []
w[N+1] = 0
for (i=0;i<N;i++){
    if (s[i] == '#') {
        bc++
    }
    if (s[N-i-1] == '.') {
        wc++
    }
    b[i+1] = bc 
    w[N-i] = wc 
}
min = Infinity
for (i=0; i<=N; i++) {
    m = b[i] + w[i+1]
    if (m < min) {
        min = m
    }
}
console.log(min)