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: Wrong Answer)

#include <stdio.h>
#define N 3*10*10*10*10*10

int main(void){

    int length, count = 0, i, j, wcount=0, bcount=0;
    char s[N];

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

    if (s[0] == '#' && s[1] == '.'){
        s[0] = '.';
        count++;
    }

    for (i=1; i<=length-3; i++){
        if (s[i] == '#' && s[i+1] == '.'){
            if (s[i-1] == '#' && s[i+2] == '#'){
                s[i+1] = '#';
                count++;
            } else if (s[i-1] == '#' && s[i+2] == '.'){
                for (j=i-1; j>=0; j--){
                    if(s[j] == '#'){
                        bcount++;
                    } else {
                        break;
                    }
                }
                for (j=i+2; j<=length-3; j++){
                    if (s[j] == '.'){
                        wcount++;
                    } else {
                        break;
                    }
                }
                if(bcount > wcount){
                    s[i+1] = '#';
                    count++;
                } else if(wcount > bcount){
                    s[i] = '.';
                    count++;
                } else {
                    s[i+1] = '#';
                    count++;
                }
            } else if (s[i-1] == '.' && s[i+2] == '#'){
                s[i+1] = '#';
                count++;
            } else if (s[i-1] == '.' && s[i+2] == '.'){
                s[i] = '.';
                count++;
            }
        }
    }

    if (s[length-2] == '#' && s[length-1] == '.'){
        s[length-1] = '#';
        count++;
    }

    printf("%d", count);

    return 0;
}