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: Time Limit Exceeded)

using System;
using System.Collections.Generic;
using System.Linq;

namespace CompetitiveProgCsLib
{
	public static class MainProg
	{
		static string R => Console.ReadLine();
		static int RI => int.Parse(R);
		static double RD => double.Parse(R);
		static int[] RIs => R.Split(' ').Select(int.Parse).ToArray();
		static double[] RDs => R.Split(' ').Select(double.Parse).ToArray();
		static void Out(object obj) => Console.WriteLine(obj);
		static void OutLine<T>(IEnumerable<T> obj, string separateChar) => Out(String.Join(separateChar, obj));
		static void Outb(bool b) => Out(b ? "Yes" : "No");
		static void OutB(bool b) => Out(b ? "YES" : "NO");
		static bool IsIn(int y, int x, int h, int w) => 0 <= x && x < w && 0 <= y && y < h;
		static T MIN<T>(params T[] args) => args.Min();
		static T MAX<T>(params T[] args) => args.Max();
		
		public static void Main(string[] args)
		{
			var n = RI;
			var s = R;
			Out(CountChar(s, "#."));
		}

		public static int CountChar(string s, string c)
		{
			int count = 0;
			while(true)
			{
				var a = s.Replace(c, "");
				var cc = (s.Length - a.Length) / c.Length;
				if (cc == 0) break;
				count += cc;
				s = a;
			}
			return count;
		}
	}
}