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

int main()
{
    int n;
    string s;
    cin >> n >> s;
    int black = 0;
    for(int i = 0; i < n; ++i)
    {
        if(s[i] == '#') ++black;
    }

    cout << min(black, s.size() - black) << endl;
}