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>

int min(int a, int b){
    return (a < b) ? a : b;
}

int main(void){
    int N;
    scanf("%d", &N);
    char s[N+1];
    scanf("%s", s);
    int countw[N+1];
    int countb[N+1];
    int min = N;
    countw[0] = (s[0] == '.');
    countb[0] = (s[0] == '#');
    int count = 0;
    for(int i = 1; i<N; i++){
        countb[i] = countb[i-1] + (s[i] == '#');
        countw[i] = countw[i-1] + (s[i] == '.');
    }
    //iをblack
    if(countb[N-1] == N){
        min = 0;
    }
    for(int i = 1; i<N; i++){
        count = countb[i-1] + (countw[N-1] - countw[i]);
        if(count < min){
            min = count;
        }
    }

    printf("%d\n", min);

    return 0; 
}