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>
#include<algorithm>
using namespace std;
#define int long long
#define str string
#define rep(x,y) for(int i=x;i<y;i++)
#define REP(x,y) for(int j=x;j<y;j++)
#define all(x) x.begin(),x.end()
signed main(){
  int A,B=0,C,N,K=0;
  str S,W,T;
  cin>>N>>S;
  rep(0,N){
    if(S.at(i)=='.'){
      if(B==0)A=N-i;
      B+=1;
    }
  }
  for(int i=N;i>N;i--){
    if(S.at(i)=='#'){
      if(N==0)C=N-1;
      K+=1;
    }
  }
  cout<<min(A-B,C-K)<<endl;
}