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 <iostream>
#include <algorithm>
#include <vector>
#include <string>
#include <map>
#include <utility>
typedef long long ll;
using namespace std;

int main(){
  ll i,j,k,n,m;
  cin >> n;
  string s,t;
  cin >> s;
  t=s;
  ll ret=0,sum=0;
  ll cnt[n]={};
  if(s[0]=='.')cnt[0]++;
  for(i=1;i<n;i++){
    if(s[i]=='.'){
      cnt[i]++;
    }
    cnt[i]+=cnt[i-1];
  }
  ret=n+10;
  for(i=1;i<n;i++){
    ret=min(i-cnt[i]+cnt[n-1]-cnt[i-1],ret);
  }
  cout << ret << endl;
  return 0;
}