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>
#include<stdlib.h>
#include<stdint.h>
#include<inttypes.h>

typedef int32_t i32;

#define MIN(a,b) ((a) < (b) ? (a) : (b))

void run (void) {
  i32 n;
  scanf ("%" SCNi32, &n);
  char *s = (char *) calloc (n + 1, sizeof (char));
  scanf ("%s", s);
  i32 w = 0;
  for (i32 i = 0; i < n; ++i) {
    if (s[i] == '.') {
      w++;
    }
  }
  i32 min = MIN(n - w, w);
  i32 b = 0;
  for (i32 i = 0; i < n; ++i) {
    if (s[i] == '.') {
      w--;
    } else {
      b++;
    }
    min = MIN(min, b + w);
  }
  printf ("%" PRIi32 "\n", min);
}

int main (void) {
  run();
  return 0;
}