#include <algorithm>
#include <climits>
#include <cmath>
#include <cstdio>
#include <cstdlib>
#include <ctime>
#include <iostream>
#include <sstream>
#include <functional>
#include <map>
#include <string>
#include <cstring>
#include <vector>
#include <queue>
#include <stack>
#include <deque>
#include <set>
#include <list>
#include <numeric>
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
typedef pair<ll,ll> P;
const double PI = 3.14159265358979323846;
const double EPS = 1e-12;
const ll INF = 1LL<<29;
const ll mod = 1e9+7;
#define rep(i,n) for(int (i)=0;(i)<(ll)(n);++(i))
#define repd(i,n,d) for(ll (i)=0;(i)<(ll)(n);(i)+=(d))
#define all(v) (v).begin(), (v).end()
#define pb(x) push_back(x)
#define mp(x,y) make_pair((x),(y))
#define mset(m,v) memset((m),(v),sizeof(m))
#define chmin(X,Y) ((X)>(Y)?X=(Y),true:false)
#define chmax(X,Y) ((X)<(Y)?X=(Y),true:false)
#define fst first
#define snd second
#define UNIQUE(x) (x).erase(unique(all(x)),(x).end())
template<class T> ostream &operator<<(ostream &os, const vector<T> &v){int n=v.size();rep(i,n)os<<v[i]<<(i==n-1?"":" ");return os;}

ll solve(const string &s, int x, int b){
	if(b==1) return INF;
	int n = s.size();
	vector<int> v(n);
	rep(i, n) v[i] = s[i]=='#'?1:-1;
	int left = n-1, right = 0;
	int cnt = 0;
	rep(i, n) if(v[i]==1){
		left = min(left, i);
		right = max(right, i);
		cnt++;
	}
	int res = 0;
	auto inc = [&]{ x++; res++; v[x] *= -1; cnt += v[x]; };
	auto dec = [&]{ x--; res++; v[x] *= -1; cnt += v[x]; };
	while(x>0 && x>left){
		dec();
		//x--; res++;	v[x] *= -1;	cnt += v[x];
	}
	if(v[x]==1){
		if(cnt==1) return 3;
		//int d = b?-1:1;
		if(x+1<0 || n<=x+1) return INF;
		inc();
		//x++; res++; v[x] *= -1; cnt += v[x];
		dec();
	}
	while(cnt){
		if(x>0 && v[x-1]==1) dec();
		else if(x<n-1) inc();
		else dec();
	}
	return res;
}

int main(){
	int n;
	string s;
	cin>>n>>s;
	n--;
	ll res = min(solve(s, n, 0), solve(s, n, 1));
	reverse(all(s));
	n = s.size()-n-1;
	res = min(res, min(solve(s, n, 0), solve(s, n, 1)));
	cout<<res<<endl;
	return 0;
}