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()
{
    long long int n,a,b,ans,c,d;
    scanf("%lld",&n);
    char s[n+1];
    scanf("%s",s);
    for(int i=n-1;i>=0;i--){
        if(s[i] == '.'){
            c=i;
            break;
        }
    }
    for(int i=0;i<n;i++){
        if(s[i] == '#'){
            d=i;
            break;
        }
    }
    for(int i=d;i<=c;i++){
        if(s[i] == '.') a++;
        else b++;
    }
    ans = (a < b) ? a : b;
    printf("%lld",ans);
}

// 白　a 黒　b