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){
  long N;
  char S[200001];
  char S2[200001];
  int min;
  int count = 0;
  int i;

  scanf("%d",&N);
  scanf("%s",S);
  
  for(i=0;i<N;i++){
    S2[i]=S[i];
  }

  for(i=0;i<N;i++){
    if(S[i]=='#'){
      if(i!=N-1){
        if(S[i+1]=='.'){
          S[i+1]='#';
          count++;
         // puts("D");
        }
      }
    }
  }

  min = count;
  count = 0;

  for(i=N-1;i>=0;--i){
  // printf("%d\n",i);
    if(S2[i]=='.'){
    //  printf("A\n");
      if(i!=0){
     //   puts("B");
        if(S2[i-1]=='#'){
      //    puts("C");
          S2[i-1]='.';
          count++;
        }
      }
    }
  }

  if(min<count){
    printf("%d",min);
  }else{
    printf("%d\n",count);
  }

  return 0;
}