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 functools import reduce
from fractions import gcd
from collections import defaultdict
import math
import bisect
import itertools
import sys
sys.setrecursionlimit(10**7)
input = sys.stdin.readline
INF = float("inf")


# 処理内容
def main():
    N = int(input())
    S = input()[:-1]

    l = 0
    r = 0
    for i in range(N):
        if S[i] == ".":
            r += 1
    
    ans = INF
    for i in range(N):
        if S[i] == "#":
            l += 1
        else:
            r -= 1
        ans = min(ans, l + r)
    
    print(ans)
    


if __name__ == '__main__':
    main()