#include <bits/stdc++.h>
using namespace std;

using VI = vector<int>;
using VVI = vector<VI>;
using PII = pair<int, int>;
using LL = long long;
using VL = vector<LL>;
using VVL = vector<VL>;
using PLL = pair<LL, LL>;
using VS = vector<string>;

#define ALL(a)  begin((a)),end((a))
#define RALL(a) (a).rbegin(), (a).rend()
#define PB push_back
#define EB emplace_back
#define MP make_pair
#define SZ(a) int((a).size())
#define SORT(c) sort(ALL((c)))
#define RSORT(c) sort(RALL((c)))
#define UNIQ(c) (c).erase(unique(ALL((c))), end((c)))

#define FOR(i,a,b) for(int i=(a);i<(b);++i)
#define REP(i,n)  FOR(i,0,n)

#define FF first
#define SS second
template<class S, class T>
istream& operator>>(istream& is, pair<S,T>& p){
  return is >> p.FF >> p.SS;
}
template<class S, class T>
ostream& operator<<(ostream& os, const pair<S,T>& p){
  return os << p.FF << " " << p.SS;
}
template<class T>
ostream& operator<<(ostream& os, const vector<T>& xs){
  for(auto& x: xs) os << x << " ";
  return os;
}
template<class T>
void maxi(T& x, T y){
  if(x < y) x = y;
}
template<class T>
void mini(T& x, T y){
  if(x > y) x = y;
}


const double EPS = 1e-10;
const double PI  = acos(-1.0);
const LL MOD = 1e9+7;

int main(){
  cin.tie(0);
  ios_base::sync_with_stdio(false);

  int b;
  cin >> b;
  --b;
  string S;
  cin >> S;
  int N = SZ(S);
  VI xs(N);
  REP(i,N){
	xs[i] = S[i] == '#';
  }

  VI ans(2, 1e9);
  REP(it,2){
	reverse(ALL(xs));
	b = N - b - 1;
	int l = -1;
	for(int i=0;i<=b;++i){
	  if(xs[i]){
		l = i;
		break;
	  }
	}
	VI tmp = xs;
	ans[it] = 0;
	if(l != -1){
	  FOR(i,l,b){
		tmp[i] ^= 1;
		ans[it]++;
	  }
	}
	else l = b;
	int ix = l;
	if(tmp[ix] == 1){
	  ans[it] += 2;
	  tmp[ix] = 0;
	  tmp[ix+1] ^= 1;
	}

	for(int i=ix+1;i<N;++i){
	  if(tmp[i]) continue;
	  bool done = true;
	  for(int j=i+1;j<N;++j)
		if(tmp[j]){
		  done = false;
		  break;
		}
	  
	  if(done){
		ans[it] += i - ix - 1;
		break;
	  }
	  ans[it] +=  i - ix + 2;
	  tmp[i+1] ^= 1;
	  ix = i;
	}
	bool done = true;
	for(int j=ix;j<N;++j)
	  if(tmp[j]){
		done = false;
		break;
	  }
	if(!done) ans[it] += N-1-ix;
  }

  cout << min(ans[0], ans[1]) << endl;

  return 0;
}