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 <iostream>
#include <vector>
#include <string>
#include <algorithm>
#include <iomanip>

//#define DEBUG
using namespace std;

int main(){
    int N;
    cin >> N;
    string S;
    cin >> S;

    vector <int> sum(N+1, 0);

    for(int i = 1; i < N; i++){
        if(S.at(i-1) == '#' && S.at(i) == '.'){
            sum.at(i+1) = sum.at(i) + 1;
        }else{
            sum.at(i+1) = sum.at(i);
        }

    }
    #ifdef DEBUG
    for(int i = 0; i < sum.size(); i++){
        cout << sum.at(i) << " ";
    }cout << endl;
    #endif
    cout << sum.at(N) << endl;

}