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: Accepted)

#include <stdio.h>

int main(void){
    int n;
    char s[200001] = {};
    int memo[200001][2] = {};
    int countf, countb, result;
    int i;
    
    scanf("%d", &n);
    scanf("%s", s);
    
    countf = 0;
    for(i = 0; i <= n; i++){
        memo[i][0] = countf;
        if(s[i] == '#'){
            countf++;
        }
    }
    
    countb = 0;
    for(i = n; i >= 0; i--){
        if(s[i] == '.'){
            countb++;
        }
        memo[i][1] = countb;
    }
    
    result = 200001;
    for(i = 0; i <= n; i++){
        if(memo[i][0] + memo[i][1] < result){
            result = memo[i][0] + memo[i][1];
        }
    }
    
    printf("%d\n", result);
    
    return 0;
}