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 all(x) x.begin(),x.end()
#define rall(x) x.rbegin(),x.rend()
#define print(s) cout << s << endl
#define acc(v) accumulate(v.begin(), v.end(), 0)
#define cinv(n,v) rep(i,n) cin >> v[i]
using namespace std;
const int INF = 1e9;
typedef long long ll;
typedef pair<int,int> pii;
typedef vector<int> vint;
typedef vector<string> vstr;
typedef vector<char> vchar;
const ll LINF = 1e18;
const ll MOD = 1e9 + 7;
int x_pos[4] = {1,0,-1,0}, y_pos[4] = {0,1,0,-1};
int ctoi(char c) {
	if (c >= '0' && c <= '9') {
		return c - '0';
	}
	return 0;
}

char upper(char c){
	return c-0x20;
}

char lower(char c){
	return c+0x20;
}

void unique_vector(vector<int>& v){
	sort(all(v));
	v.erase(unique(all(v)), v.end());
}

// n次元配列の初期化。第２引数の型のサイズごとに初期化していく。
template<typename A, size_t N, typename T>
void Fill(A (&array)[N], const T &val){
    std::fill( (T*)array, (T*)(array+N), val );
}

int main() {
    int n;cin >> n;
    string s;cin>>s;
    int w_cnt= 0;
    rep(i,n)if(s[i]=='.')w_cnt++;
    int b_cnt = 0;
    int ans = INF;
    rep(i,n){
        if(s[i]=='#')b_cnt++;
        else w_cnt--;
        ans = min(ans,b_cnt+w_cnt);
    }
    cout << ans << endl;
}