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; 
using ll = long long;
using ull = unsigned long long;
using pii = pair<int,int>; 

#define INF 100000000
#define MOD 998244353
#define rng(a) a.begin(),a.end()
#define rrng(a) a.rbegin(),a.rend()

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

  int ans1=0;
  int c=0;
  for(int i=0;i<N;i++){
    if(s[i]=='#')c++;
    else {
      ans1+=c;
      c=0;
    }
  }

  int ans2=0;
  c=0;
  for(int i=N-1;i>=0;i--){
    if(s[i]=='.')c++;
    else{
      ans2+=c;
      c=0;
    }
  }

  int ans=min(ans1,ans2);
  cout<<ans<<endl;
  return 0;
}