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 C# (Mono 4.6.2.0) (judge verdict: Accepted)

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;

namespace Miscelleneous {
	class Program {
		static int[] parins() {
			return Console.ReadLine().Split(' ').Select(s => int.Parse(s)).ToArray();
		}
		static void Main(string[] args) {
			Console.ReadLine();
			var S = Console.ReadLine();
			var Stones = Parse(S);
			Console.WriteLine(calc(Stones));
		}

		static bool[] Parse(string d) {
			return d.Select(c => c == '#').ToArray();
		}

		static int calc(bool[] Blacks) {
			var N = Blacks.Length;
			int I;  //Count for Change into (index) of White leftside and rest Black rightside
			I = Blacks.Count(b => !b);
			int res = I;
			for (int i = 0; i < N; i++) {
				if (Blacks[i]) I++;
				else {
					I--;
					if (I < res) res = I;
				}
			}
			return res;
		}
	}

}