#include<bits/stdc++.h>
using namespace std;
#define rep(i,n) for(ll i=0;i<n;i++)
#define repl(i,l,r) for(ll i=(l);i<(r);i++)
#define per(i,n) for(ll i=(n)-1;i>=0;i--)
#define perl(i,r,l) for(ll i=r-1;i>=l;i--)
#define fi first
#define se second
#define ins insert
#define pqueue(x) priority_queue<x,vector<x>,greater<x>>
#define all(x) (x).begin(),(x).end()
#define CST(x) cout<<fixed<<setprecision(x)
#define rev(x) reverse(x);
using ll=long long;
using vl=vector<ll>;
using vvl=vector<vector<ll>>;
using pl=pair<ll,ll>;
using vpl=vector<pl>;
using vvpl=vector<vpl>;
const ll MOD=1000000007;
const ll MOD9=998244353;
const int inf=1e9+10;
const ll INF=4e18;
const ll dy[9]={1,0,-1,0,1,1,-1,-1,0};
const ll dx[9]={0,1,0,-1,1,-1,1,-1,0};
template <typename T> inline bool chmax(T &a, T b) {
  return ((a < b) ? (a = b, true) : (false));
}
template <typename T> inline bool chmin(T &a, T b) {
  return ((a > b) ? (a = b, true) : (false));
}
ll ans=INF;
void solve(vl v,ll p){
  ll n=v.size();
  ll left=INF;
  rep(i,n){
    if(v[i]==1)chmin(left,i);
  }
  if(left>=p){
    return;
  }
  ll ret=p-left;
  for(ll x=left;x<p;x++)v[x]^=1;
  ll right=-INF;
  rep(i,n)if(v[i]==1)chmax(right,i);
  //rep(i,n)cout << v[i];cout << endl;
  for(ll x=left;x<right;x++){
    if(x==right-1&&v[right]==0)continue;
    if(v[x+1]==1){
      v[x+1]^=1;
      ret++;
    }
    else{
      ret+=3;
      v[x+2]^=1;
    }
    //rep(i,n)cout << v[i];cout << endl;cout << ret << endl;
  }
  //rep(i,n)cout << v[i];cout << endl;
  chmin(ans,ret);
}

int main(){
  ll n;cin >> n;
  string s;cin >> s;
  vl v(s.size());
  rep(i,s.size())if(s[i]=='#')v[i]=1;
  solve(v,n-1);
  rev(all(v));
  solve(v,s.size()-n);
  if(ans==INF){
    cout << 3 << endl;
  }
  else cout << ans << endl;
}