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 (GCC 5.4.1) (judge verdict: Wrong Answer)

#include<stdio.h>

int count_rightwhite(int i,int n,const char s[])
{
  int cnt=0;
  int j;
  for(j=i;j<n;j++){
    if(s[j]=='.')cnt++;
  }
  return cnt;
}


int main(void)
{
  int n;
  char s[200001];
  scanf("%d",&n);
  scanf("%s",s);
  
  int c[200001]={0};
  int i=0,j=0;
  for(i=0;i<n;i++){
    if(j%2==0){
      if(s[i]=='.'){
        c[j]++;
      }else{
        j++;
        c[j]++;
      }
    }else{
      if(s[i]=='#'){
        c[j]++;
      }else{
        j++;
        c[j]++;
      }
    }
  }
  
  int cntmin=n;
  int sum_black=0,sum_white=count_rightwhite(0,n,s);
  for(i=0;i<=j;i+=2){
    sum_white-=c[i];
    
    int tmp=sum_black+sum_white;
    if(cntmin>tmp){
      cntmin=tmp;
      printf("%d\n",i);
    }
    
    sum_black+=c[i+1];
  }
  
  printf("%d\n",cntmin);
  return 0;
}