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>
 
long long min (long long a,long long b)
{
    if(a > b)   return b;
    else return a;
}
int main (void) 
{
    long int n;
    scanf("%ld", &n);
    char s[n + 1];
    scanf("%s",s);
    long int i;
    long int size = 1;
    for (i = 0; i < n -1; i ++)    {
        if(s[i] != s[i + 1])    size ++;
    }
    long int  b[size];
    for (i = 0; i < size ; i ++) {
        b[i] = 1;
    }
    long int j = 0;
    for (i = 0; i < n-1 ; i++)    {
        if(s[i+1] == s[i])  b[j] ++;
        else j ++;
    }
 
    long int ans = 0;
    if(s[0] == '#') {
        for (i = 0 ; i < size -1 ; i += 2)  {
          ans += min (b[i],b[i + 1]);
        }
    }
    else
    {
        for(i = 1; i < size -1 ; i+= 2) {
            ans += min (b[i],b[i+1]);
        }
    }
    printf("%ld",ans);
}