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 (Clang 3.8.0) (judge verdict: Wrong Answer)

#include <stdio.h>

int main(int argc, char const *argv[])
{
    int N;
    scanf("%d",&N);
    char S[N];
    scanf("%s",S);
    int B,W;
    int b[N],w[N];
    
    if (S[0]=='#'){b[0]=1;B++;}else{b[0]=0;W++;}

    for (size_t i = 1; i < N; i++){
        if (S[i]=='#'){
            b[i]=b[i-1]+1;
            B++;
        }else{
            b[i]=b[i-1];
            W++;
            }
    }

    for (size_t i = 0; i < N; i++){
        w[i]=i+1-b[i];
    }

    int ans=B;
    if (ans>W){ans=W;}

    for (size_t i = 0; i < N-1; i++){
        if (ans>b[i]+w[N-1]-w[i]){
            ans=b[i]+w[N-1]-w[i];
        }
    }
    printf("%d\n",ans);
    return 0;
}