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(void){

  int n;
  scanf("%d", &n);
  char s[n];
  scanf("%s", s);
  int black[n];
  black[0] = 0;
  if (s[0] == '#') {
    black[0]++;
  }
  for (int i = 1; i < n; i++) {
    black[i] = black[i-1];
    if (s[i] == '#') {
      black[i]++;
    }
  }
  int min = n-black[n-1];
  int change;
  for (int i = 0; i < n; i++) {
    change = black[i] + n-i-1-(black[n-1]-black[i]);
    if (change < min) {
      min = change;
    }
  }
  printf("%d\n", min);

  return 0;
}