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: Accepted)

#include <stdio.h>

int main()
{
  int n, blacks = 0, s[200000] = { }, currentblack_white = 0, maxblack_white = 0;
  scanf("%d\n", &n);
  for (int i = 0; i < n; i++) {
    if (getchar() == '#') {
      blacks++;
      s[i] = 1;
    }
  }
  for (int i = n - 1; i >= 0; i--) {
    if (s[i] == 1) {
      currentblack_white++;
      if (currentblack_white > maxblack_white) {
        maxblack_white = currentblack_white;
      }
    } else {
      currentblack_white--;
    }
  }
  printf("%d\n", blacks - maxblack_white);
  return 0;
}