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 (GCC 5.4.1) (judge verdict: Accepted)

#include <bits/stdc++.h>
#define be(v) (v).begin(),(v).end()
#define pb(q) push_back(q)
#define era(t) t.erase(unique(be(t)),t.end())
#define doublecout(a) cout<<fixed<<setprecision(10)<<a<<endl;
typedef long long ll;
using namespace std;
const ll mod=1000000007,mod9=1000000009;
template <class T>inline T lcm(T a,T b){return (a*b/__gcd(a,b));}

int main() {
    cin.tie(0);
    ios::sync_with_stdio(false);
    int n,ans=1e9,num;
    string s;
    cin>>n>>s;
    int a[n+1];
    a[0]=0;
    for(int i=0;i<n;i++){
        if(s[i]=='#'){
            a[i+1]=a[i]+1;
        }
        else{
            a[i+1]=a[i];
        }
    }
    for(int i=0;i<=n;i++){
        num=a[i];
        num+=(n-i)-(a[n]-a[i]);
        ans=min(ans,num);
    }
    cout << ans<<endl;
    return 0;
}