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 Python (3.4.3) (judge verdict: Wrong Answer)

from collections import defaultdict
from string import ascii_uppercase
import sys, bisect, math,string
stdin = sys.stdin
read_int = lambda : list(map(int,stdin.readline().split()))
read_str = lambda : stdin.readline().rstrip()

N = read_int()[0]
S = read_str()

def solve():
    ans = 0
    head_dot = 0
    tail_hash = N
    for i in range(N):
        if S[i] != ".":
            break
        head_dot += 1
    for i in range(N):
        if S[N - i -1] != "#":
            break
        tail_hash -= 1
    if head_dot < tail_hash:
        ans = min(S[head_dot:tail_hash+1].count("."), S[head_dot:tail_hash+1].count("#"))
    return ans

if __name__ == "__main__":
    print(solve())