#include <bits/stdc++.h>
using namespace std;
 
int main() {
int N;string S;int count;int kuro;int siro;
  cin>>N; cin >>S;
  count=0;kuro=0;siro=0;
  
  for (int i = 0; i < N-1; i++) {  
   if(S.at(i)=='#'){
     
     for (int i = 0; i < N-i; i++) {
     if(S.at(i)=='#'){kuro=kuro+1;}
       else{siro=siro+1}
     }
     
     if(kuro>=siro){
     S.at(i+1)='#';
     count=count+1;
     }
   }    
  } 
  if(kuro<siro){
     cout<<siro<<endl;
     }else{
 cout<<count<<endl;
  }
}
