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;
  char S[200001];
  scanf("%d", &N);
  scanf("%s", S);

  int X = 0;
  int B = 0;
  int W = 0;
  if(S[0] == '#') B++;
  else W++;
  for(int i = 1; i < N; i++) {
    //printf("i=%d B=%d W=%d X=%d\n", i, B, W, X);
    if(S[i] == '#') {//Black
      if(S[i-1] == '#') {
	B++;
      } else {
	B = 1;
	W = 0;
      }
      continue;
    }
    // White
    if(S[i-1] != '#') {// White
      W++;
      continue;
    }

    // Black->White
    W = 1;
    int j;
    for(j = i+1; j < N; j++) {
      if(S[j] == '#') break;
      W++;
    }
    //printf("i=%d B=%d W=%d X=%d -> %d\n", i, B, W, X, X + ((B<W) ? B : W));
    if(B <= W) {
      X += B;
      i = j-1;
      W += B;
      B = 0;
    } else {
      X += W;
      S[j-1] = '#';
      i = j-1;
      B += W;
      W = 0;
    }
  }

  printf("%d\n", X);
  return 0;
}