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 (Clang 3.8.0) (judge verdict: Accepted)

#include<stdio.h>
#include<string.h>
#include<math.h>
int main(void) {
	int n,w = 0,b = 0;
	scanf("%d", &n);
	char s[n + 1];
	scanf("%s", s);
	for (int i = 0;i < n;i++) {
		if (s[i] == '.') {
			w++;
		}
	}
	if (w == 0 || w == n) {
		printf("0");
		return 0;
	}
	int ans = w;
	for (int i = 0;i < n;i++) {
		if (s[i] == '.') {
			w--;
		}
		else {
			b++;
		}
		if (ans > w + b) {
			ans = w + b;
		}
	}
	printf("%d", ans);
	return 0;
}