#include <bits/stdc++.h>
using namespace std;
#define F first
#define S second
#define R cin>>
#define Z class
#define ll long long
#define ln cout<<'\n'
#define in(a) insert(a)
#define pb(a) push_back(a)
#define pd(a) printf("%.10f\n",a)
#define mem(a) memset(a,0,sizeof(a))
#define all(c) (c).begin(),(c).end()
#define iter(c) __typeof((c).begin())
#define rrep(i,n) for(ll i=(ll)(n)-1;i>=0;i--)
#define REP(i,m,n) for(ll i=(ll)(m);i<(ll)(n);i++)
#define rep(i,n) REP(i,0,n)
#define tr(it,c) for(iter(c) it=(c).begin();it!=(c).end();it++)
template<Z A>void pr(A a){cout<<a;ln;}
template<Z A,Z B>void pr(A a,B b){cout<<a<<' ';pr(b);}
template<Z A,Z B,Z C>void pr(A a,B b,C c){cout<<a<<' ';pr(b,c);}
template<Z A,Z B,Z C,Z D>void pr(A a,B b,C c,D d){cout<<a<<' ';pr(b,c,d);}
template<Z A>void PR(A a,ll n){rep(i,n){if(i)cout<<' ';cout<<a[i];}ln;}
ll check(ll n,ll m,ll x,ll y){return x>=0&&x<n&&y>=0&&y<m;}
const ll MAX=1000000007,MAXL=1LL<<61,dx[4]={-1,0,1,0},dy[4]={0,1,0,-1};
typedef pair<int,int> P;

void Main() {
  int n,m;
  string s;
  cin >> n >> s;
  n--;
  m=s.size();
  int ans=MAX;
  rep(k,2) {
    int x=n,sum=0,y=0,cnt=0;
    int d[m],c[m];
    mem(c);
    rep(i,m) {
      if(s[i]=='#') d[i]=1;
      else d[i]=0;
    }
    rrep(i,n) if(d[i]) x=i;
    REP(i,n,m) {
      if(d[i]) {
        y=i;
        cnt++;
      }
    }
    REP(i,x,n) {
      c[i]=1;
      if(d[i]!=c[i]) cnt++;
      sum++;
    }
    REP(i,x+1,y+1) {
      if(!cnt) break;
      sum++;
      c[i]^=1;
      if(d[i]!=c[i]) {
        cnt++;
        c[i]^=1;
        c[i+1]^=1;
        if(c[i+1]!=d[i+1]) cnt++;
        else cnt--;
        sum+=2;
      }
      cnt--;
      if(cnt==abs(y-i)) {
        sum+=abs(y-i);
        break;
      }
    }
    ans=min(ans,sum);
    reverse(all(s));
    n=m-n-1;
  }
  pr(ans);
}

int main(){ios::sync_with_stdio(0);cin.tie(0);Main();return 0;}