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

int main()
{
  int n;
  string s;
  cin >> n >> s;
  int i;
  int point = 1000000;
  int countb = 0;
  int countw = 0;
  int ch = 0;
  for(i = 0; i < n; i++)
  {
    if(s.at(i) == '#')
    {
      point = i;
      break;
    }
  }
  if(point == 1000000)
  {
    ch = 1;
  }
  else
  {
    for(i = point; i < n; i++)
    {
      if(s.at(i) == '#')
      {
        countb++;
      }
      else
      {
        countw++;
      }
    }
  }
  /*if(ch == 1)
  {*/
    cout << 0 << endl;
  }/*
  else
  {
    cout << min(countb, countw) << endl;
  }*/
}
