#include <cstdio>
#include <cstring>
#include <iostream>
#include <string>
#include <cmath>
#include <bitset>
#include <vector>
#include <map>
#include <set>
#include <queue>
#include <deque>
#include <algorithm>
#include <complex>
#include <unordered_map>
#include <unordered_set>
#include <random>
#include <cassert>
#include <fstream>
#include <utility>
#include <functional>
#define popcount __builtin_popcount
using namespace std;
typedef long long int ll;
typedef pair<int, int> P;
const int INF=1e8;
int solve(string s, int k){
	int n=s.size();
	int l=k, r=-1;
	for(int i=0; i<k; i++){
		if(s[i]=='#'){
			l=i; break;
		}
	}
	for(int i=l; i<k; i++){
		if(s[i]=='#') s[i]='.';
		else s[i]='#';
	}
	for(int i=n-1; i>=0; i--){
		if(s[i]=='#'){
			r=i; break;
		}
	}
	if(r==-1){
		return k-l;
	}
	int dp[2][2][100010];
	for(int i=0; i<2; i++) for(int j=0; j<2; j++) for(int m=0; m<n; m++) dp[i][j][m]=INF;
	if(s[l]=='#') dp[0][1][l]=3;
	else dp[0][0][l]=1;
	for(int i=l; i<n-1; i++){
		if(s[i+1]=='#'){
			dp[0][0][i+1]=min(dp[0][0][i+1], dp[0][0][i]+1);
			dp[0][1][i+1]=min(dp[0][1][i+1], dp[0][1][i]+3);
			dp[1][0][i+1]=min(dp[1][0][i+1], dp[1][1][i]+2);
			dp[1][1][i+1]=min(dp[1][1][i+1], dp[1][0][i]+4);
			dp[1][0][i+1]=min(dp[1][0][i+1], dp[0][1][i]+2);
			dp[1][1][i+1]=min(dp[1][1][i+1], dp[0][0][i]+4);
		}else{
			dp[0][0][i+1]=min(dp[0][0][i+1], dp[0][1][i]+1);
			dp[0][1][i+1]=min(dp[0][1][i+1], dp[0][0][i]+3);
			dp[1][0][i+1]=min(dp[1][0][i+1], dp[1][0][i]+2);
			dp[1][1][i+1]=min(dp[1][1][i+1], dp[1][1][i]+4);
			dp[1][0][i+1]=min(dp[1][0][i+1], dp[0][0][i]+2);
			dp[1][1][i+1]=min(dp[1][1][i+1], dp[0][1][i]+4);
		}
	}
	int ans=INF;
	for(int i=n-1; i>=1; i--){
		if(s[i]=='#'){
			ans=min({ans, dp[1][0][i-1]+k-l, dp[0][0][i-1]+k-l});
			break;
		}else{
			ans=min({ans, dp[1][1][i-1]+k-l, dp[0][1][i-1]+k-l});
		}
	}
	return ans;
}
int main()
{
	int k; cin>>k; k--;
	string s; cin>>s;
	int n=s.size();
	int ans=solve(s, k);
	reverse(s.begin(), s.end());
	k=n-1-k;
	ans=min(ans, solve(s, k));
	cout<<ans<<endl;
	return 0;
}