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;
    char s[200001];

    int b, w;
    int i, j, k, p, min, num, stock_a, stock_b;

    scanf("%d", &n);
    scanf("%s", s);

    b = 0;
    w = 0;

    for(i=0;i<n;i++){
        if(s[i] == '#'){
            break;
        }
    }
    k = i;

    for(i=n-1;i>=0;i--){
        if(s[i] == '.'){
            break;
        }
    }
    j = i;

    //printf("%d %d\n", k, j);

    min = j - k + 1;
    stock_a = 0;
    stock_b = 0;
    for(p=k;p<=j;p++){
        if(s[p] == '.'){
            stock_b++;
        }
    }

    for(p=k;p<=j;p++){
        if(s[p] == '#'){
            stock_a++;
        }
        if(s[p] == '.'){
            stock_b--;
        }
        if(p == k){
            num = stock_b;
        }else{
            num = stock_a + stock_b;
        }
        if(num < min){
            min = num;
        }
        //printf("%d\n", num);
    }

    printf("%d", min);

    return 0;
}