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++14 (GCC 5.4.1) (judge verdict: Wrong Answer)

#include <bits/stdc++.h>
#include <array>
#define FOR(i,a,b) for(int i=(a);i<=(b);++i) 
#define RFOR(i,a,b) for(int i=(a);i>=(b);--i) 
#define REP(i,n) for(int i=0;i<(n);++i)
#define RREP(i,n) for(int i=(n);i>0;--i)
#define CI cin>> 
#define CO cout<<
#define EN <<endl 
#define all(x) (x).begin(),(x).end() 
using namespace std;
template <typename T> istream & operator >> (istream & is, vector<T> & vec) { for (T& x : vec) is >> x; 	return is; }
using ll = long long;
using VI = vector<int>;

int main() {
	int n; string s; CI n >> s;
	int white = 0,ans=1000000;
	string tmp = s;

	REP(i, n) {
		if (s[i] == '.')white++;
	}
	ans = min(ans, white);
	REP(i, n) {
		if (s[i] == '#')white++;
		if (s[i] == '.')white--;
		ans = min(ans, white);
	}

	CO white EN;

	return 0;
}