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 main(void){
    int N;
     scanf("%d", &N);
    char S[N];
    scanf("%s", S);
  int i;
  int existBW =0;
  
  for(i=0;i<N-1;i++){
	if(S[i] == '#'){
      if(S[i+1] == '.'){
        existBW = 1;
      }
    }
  }
  printf("existBW : %d", existBW);
  if(existBW == 1){
  int countB =0;
  int countW =0;
    int checkB = 0;
    int checkC = 0;
  for(i = 0;i<N;i++){
	if(S[i] =='#'){
      countB++;
      if(checkB == 0){
       checkB = i; 
      }
    }
    if(S[i] =='.'){
      countW++;
      if(i > checkB ){
        checkC = 1;
      }
    }
  }
    if(S[0] == '.' && checkC == 1){
    	countW = countW - checkB;
    }
  if(countB >= countW){
  	printf("%d",countW);
	return 0;
  }
   printf("%d",countB);
    return 0;
  }//if(existBW)
  
    
    printf("0");
}