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>
#define N 2*10*10*10*10*10 + 1

int main(void){

    int length, ans = 0, wnum, bnum = 0;
    char stone[N];

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

    for(int i=0; i<length; i++){
        if(stone[i] == '.'){
            ans++;
        }
    }

    wnum = ans;

    for(int i=0; i<length; i++){
        if(stone[i] == '#'){
            bnum++;
        } else {
            wnum--;
        }

        if((bnum + wnum) < ans){
            ans = (bnum + wnum);        
        }
    }

    printf("%d", ans);

    return 0;
}