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>

void solve(int len, char *str) {
    int l_b = 0, r_w = 0, i, min = 200100;
    for(i = 0; i < len; ++i) {
        if(str[i] == '.') { ++r_w; }
    }
    if(l_b + r_w < min) { min = l_b + r_w; }
    for(i = 0; i < len; ++i) {
        if(str[i] == '.')       { --r_w; }
        else if(str[i] == '#')  { ++l_b; }
        if(l_b + r_w < min) { min = l_b + r_w; }
    }
    printf("%d\n", min);
}

int main()
{
    int n;
    scanf("%d", &n);
    char *str = (char*)malloc((n+100)*sizeof(char));
    scanf("%s", str);
    solve(n, str);
    return 0;
}