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: Time Limit Exceeded)

#include<stdio.h>
int main(){
    int n,i,j,f,q,r;
    char s[200002]; 
    scanf("%d%s",&n,s);
    int c[200001]={},m=1;
    r=n;
    for(i=0;i<n-1;i++){
        c[m]++;
        if(s[i]!=s[i+1])m++;
    }
    if(s[n-1]!=s[n])c[m]++;
    if(s[0]=='#')i=f=0;
    else i=f=1;
    for(;i<=m;i+=2){
        q=0;
        for(j=f+1;j<i;j+=2)q+=c[j];
        for(j=i+2;j<=m;j+=2)q+=c[j];
        if(q<r)r=q;
    }
    printf("%d",r);
    return 0;
}