#include<bits/stdc++.h>

using namespace std;

typedef long long ll;
typedef pair<int, int> PII;

const int MM = 1e9 + 7;
const double eps = 1e-8;
const int MAXN = 2e6 + 10;

int n, m;

void prework(){

}

void read(){

}

char s[MAXN];
int f[MAXN];

int gao(int x){
	for (int i = 1; i <= n; i++)
		f[i] = (s[i] == '#');
	int st = 0;
	for (int i = 1; i <= n; i++)
		if (f[i] == 1){
			st = i;
			break;
		}
	int ed = n + 1;
	for (int i = n; i >= 1; i--)
		if (f[i] == 1){
			ed = i;
			break;
		}
	int ret = 0;
	if (x > st){
		for (x--; x >= st; x--){
			ret++;
			f[x] = 1 - f[x];
			//cout << ret << ' ' << x << endl;
		}
		x++;
	}
	f[n + 1] = 1;
	f[n + 2] = 0;
	//cout << "!!!!  " << st << ' ' << ed << ' ' << ret << ' ' << x << endl;
	while(true){
		if (f[x] == 0){
			ret++;
			x++;
			f[x] = 1 - f[x];
			//cout << ret << ' ' << x << endl;
		}
		else{
			if (x == n){
				ret += 3;
				break;
			}
			ret++;
			x++;
			f[x] = 1 - f[x];
			//cout << ret << ' ' << x << endl;
			ret++;
			x--;
			f[x] = 1 - f[x];
			//cout << ret << ' ' << x << endl;
		}
		if (x >= ed - 1 && f[x] == 0 && (f[x + 1] == 0 || x == n))
			break;
	}
	//cout << "===========  " << ret << endl;
	return ret;
}

void solve(int casi){
//	cout << "Case #" << casi << ": ";
	scanf("%d", &m);
	scanf("%s", s + 1);
	n = strlen(s + 1);
	int ans = gao(m);
	reverse(s + 1, s + n + 1);
	ans = min(ans, gao(n + 1 - m));
	printf("%d", ans);
}

void printans(){

}


int main(){
//	std::ios::sync_with_stdio(false);
	prework();
	int T = 1;
//	cin>>T;
	for(int i = 1; i <= T; i++){
		read();
		solve(i);
		printans();
	}
	return 0;
}