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;

#define INIT std::cin.tie(0);std::ios::sync_with_stdio(false);
#define ALL(c) (c).begin(), (c).end()
#define CALL(c) (c).cbegin(), (c).cend()
#define RALL(c) (c).rbegin(), (c).rend()
#define CRALL(c) (c).crbegin(), (c).crend()
#define REP(i, n) for (int i = 0; i < static_cast<int>(n); i++)
#define FOR(i, s, n) for (int i = s; i < static_cast<int>(n); i++)
#define ASC(t) [](t& x, t& y){ return x < y; }
#define DESC(t) [](t& x, t& y){ return x > y; }
#define PSORT(s,p,e) partial_sort((s), next((s), (p)), (e))
#define VIEW(v,t) for_each((v).begin(), (v).end(), [](t& a) { cout << a << " "; }); cout << endl;

#define IN(a, x, b) (a<=x && x<b)
template<class T> inline T CHMAX(T& x, const T y){return x=(x<y)?y:x;}
template<class T> inline T CHMIN(T& x, const T y){return x=(x>y)?y:x;}
#define OUT(dist) std::cout<<(dist);
#define WS std::cout<<" ";
#define NL std::cout<<"\n"

using PII = pair<int, int>;
using PLL = pair<long long, long long>;
using LL = long long;
using ULL = unsigned long long;
template<class T> using V = vector<T>;
template<class T> using V2 = vector<vector<T>>;
template<class T, int W=255> using A = array<T, W>;
template<class T, int W=255, int H=255> using A2 = array<array<T, W>, W>;

int N;
std::string s;

int main(){
    INIT;
    cin >> N; cin >> s;

    int ans = N+1;
    int m1 = 0;
    int m2 = 0;
    FOR(i, 0, N) if(s[i] == '.') m2++;
    if(m2 == N || m2 == 0) ans = 0;

    FOR(i, 0, N-1) {
        if(s[i] == '#') m1++;
        if(s[i] == '#' && s[i+1] == '.') CHMIN(ans, m1+m2);
        if(s[i] == '.' && s[i+1] == '#') CHMIN(ans, m1+m2);
        if(s[i+1] == '.') m2--;
    }

    cout << ans << "\n";
}