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 PyPy3 (2.4.0) (judge verdict: Accepted)

import sys
import os
if sys.platform=="darwin":
	base = os.path.dirname(os.path.abspath(__file__))
	name = os.path.normpath(os.path.join(base, '../Documents/input.txt'))
	#print(name)
	sys.stdin = open(name)

n = int(input())
l = input()

#print(l)
lsh = []*(n+1)
lsh.append(0)
sharp = 0
comma = 0

for i in range(n):
	if l[i]=="#":
		sharp = sharp + 1
	lsh.append(sharp)
#print(lsh)

for i in range(n-1,-1,-1):
	#print(i)
	if l[i]==".":
		comma = comma + 1
	lsh[i] = lsh[i] + comma

print(min(lsh))