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(){
    int N;
    scanf("%d", &N);

    int ans = 0, i, j;
    char S[N];
    scanf("%s", &S);

    int bnum[N], tmp=0, wht=0, max_sequence, cnt=0;
    double max=0.0;
    for (i=N-1; i>=0; i--){
        if (S[i] == '#'){
            tmp++;
        }else{
            wht++;
        }
        bnum[i] = tmp;
        if ( bnum[i] - wht > max){
            max = bnum[i] - wht;
            max_sequence = i;
        }
    }

    if (tmp != 0){
        for (i=0; i<N; i++){
            if (i<max_sequence){
                if (S[i] != '.') ans++;
            }else{
                if (S[i] != '#') ans++;
            }
        }
    }

    printf("%d", ans);
 
    return 0;
}