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 main(void){
    int N=0,i=0,W=0,B=0,ans=0;
    scanf("%d\n",&N);
    char S[N+1];
    scanf("%s",S);
    
    for(i = 0; i < N; i++){
        if(S[i]=='.'){
            W++;
        }else{
            B++;
        }
    }
    
    for(i = 0; i < N; i++){
        if(S[i]=='#'&&S[i+1]=='.'){
            if(i < N&&S[i+1]==S[i+2]){
                S[i]=='.';
                ans++;
            }else{
                S[i+1]='#';
                ans++;
            }
        }
    }
    
    printf("%d",ans);
    
    return 0;
}