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 9.2.1) (judge verdict: Wrong Answer)

#include <bits/stdc++.h>
using namespace std;
#define REP(i, n) for (int i = 0; i < (int)(n); i++)
typedef long long ll;
typedef pair<int, int> P;
int main() {
  int N;
  string S;
  cin >> N >> S;
  ll ans = 1e10;
  vector<ll> wa(N + 1);
  wa[0] = 0;
  for (int i = 1; i <= N; i++) {
    wa[i] = wa[i - 1];
    if (S[i - 1] == '.') wa[i]++;
  }
  for (int i = 1; i <= N; i++) {
    ll l = wa[i];
    ll r = wa[N] + wa[i];
    ans = min(ans, (i - l) + (r));
  }
  ans = min(wa[N], N - wa[N]);
  cout << ans << endl;
}