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++14 (Clang 3.8.0) (judge verdict: Runtime Error)

#include <algorithm>
#include <iostream>
#include <string>
using namespace std;
using int_t = long long int;
const int_t LARGE = 1e5;
char buf[LARGE * 10 + 1];
int_t prefix[2][LARGE + 1];
int main() {
    int n;
    cin >> n;
    scanf("%s", buf + 1);
    for (int_t i = 1; i <= n; i++) {
        prefix[0][i] = prefix[0][i - 1];
        prefix[1][i] = prefix[1][i - 1];

        if (buf[i] == '.')
            prefix[0][i]++;
        else
            prefix[1][i]++;
    }
    int_t result = 0x7ffffffff;
    for (int_t i = 1; i <= n; i++) {
        result =
            std::min(prefix[1][i] + prefix[0][n] - prefix[0][i], result);
        // cout << "at " << i << " = "
        //      << prefix[1][i] + prefix[0][n] - prefix[0][i - 1] << endl;
        // cout << prefix[1][i] << " " << prefix[0][n] - prefix[0][i - 1] << endl;
    }
    cout << result << endl;
    return 0;
}