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: Runtime Error)

#include <bits/stdc++.h>
using namespace std;

int main() { 
  int N;
  string S;
  int nn=0;
  int ans=10000000;
  vector<int> black(N);
  vector<int> white(N);
  cin >> N >> S ;
  
  if( S.at(0) == '#'){
      black.at(0)=1;
    }
    else{
      black.at(0)=0;
    }
  for(int i=1; i<N; i++){
    if( S.at(i) == '#'){
      black.at(i) = black.at(i-1) + 1;
    }
    else{
       black.at(i) = black.at(i-1);
    }
  }//forowari
  if (S.at(N-1) == '.'){
    white.at(N-1)=1;
  }
  else{
    white.at(N-1)=0;
  }
  for(int i = (N-2); i>=0; i--){
    if(S.at(i)=='.'){
       white.at(i) = white.at(i+1) + 1;
    }
    else{
           white.at(i) = white.at(i+1);
    }
  }
  for(int i=0; i<(N-1); i++){
    if( (S.at(i) == '.')&(S.at(i+1) == '#') ){
      int aa;
      aa = black.at(i) + white.at(i+1);
      ans = min(ans, aa);
      nn++;
    }
  }
  if(nn==0){
    ans = min (black.at(N-1) , white.at(0));
  }
  
    cout<<ans<<endl;
 
  }