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>

#define rep(i, n) for(int i = 0; i<(n); i++)
#define chmax(x, y) x = max(x, y)
#define chmin(x, y) x = min(x, y)
using namespace std;
using ll = long long;

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

    int ans = N;
    int cnt = 0;
    bool black = false;
    rep(i, S.size()) {
        if (S[i] == '#') black = true;
        if (black && S[i] == '.') cnt++;
    }
    chmin(ans, cnt);

    bool white = false;
    cnt = 0;
    for (int i = S.size() - 1; i >= 0; i--) {
        if (S[i] == '.') white = true;
        if (white && S[i] == '#') cnt++;
    }
    chmin(ans, cnt);
    cout << ans << endl;
}