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>

using namespace std;

typedef long long ll;
typedef vector<int> vint;
typedef pair<int, int> pii;

#define rep(i, n) REP(i, 0, (n))
#define REP(i, a, n) for(int i=(a); i<(n); i++)
#define pb push_back


int main() {
    int n; cin >> n;
    string s; cin >> s;
    
    int ans = 0;
    int cnt_w = 0, cnt_b = 0;
    rep(i, n/2) {
        if(s[i] == '#') {
            cnt_b++;
        } else {
            ans += cnt_b;
            cnt_b = 0;
        }
        if(s[n-i-1] == '.') {
            cnt_w++;
        } else {
            ans += cnt_w;
            cnt_w = 0;
        }
    }
    
    cout << ans << endl;
}