#include <algorithm>
#include <iostream>
#include <numeric>
#include <string>
#include <tuple>
#include <utility>
#include <vector>
#include <limits>

#define rep(i, a, b) for (int i = int(a); i < int(b); i++)
using namespace std;
using ll = long long int;  // NOLINT
using P = pair<ll, ll>;

// clang-format off
#ifdef _DEBUG_
#define dump(...) do{ cerr << __LINE__ << ":\t" << #__VA_ARGS__ << " = "; debug_print(__VA_ARGS__); } while(false)
template<typename T, typename... Ts> void debug_print(const T &t, const Ts &...ts) { cerr << t; ((cerr << ", " << ts), ...); cerr << endl; }
#else
#define dump(...) do{ } while(false)
#endif
template<typename T> vector<T> make_v(size_t a, T b) { return vector<T>(a, b); }
template<typename... Ts> auto make_v(size_t a, Ts... ts) { return vector<decltype(make_v(ts...))>(a, make_v(ts...)); }
template<typename T> bool chmin(T &a, const T& b) { if (a > b) {a = b; return true; } return false; }
template<typename T> bool chmax(T &a, const T& b) { if (a < b) {a = b; return true; } return false; }
template<typename T, typename... Ts> void print(const T& t, const Ts&... ts) { cout << t; ((cout << ' ' << ts), ...); cout << '\n'; }
template<typename... Ts> void input(Ts&... ts) { (cin >> ... >> ts); }
template<typename T> istream &operator,(istream &in, T &t) { return in >> t; }
struct Inf { template<typename T> constexpr operator T() { return numeric_limits<T>::max() / 2; } };
// clang-format on

int main() {
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    int n;
    string s;
    cin, n, s;
    reverse(s.begin(), s.end());
    auto native = [](string s, int n) {
        int ans = 0;
        rep(i, 0, 2 * n) {
            string t = s;
            if (t.front() == '#') t.front() = '.';
            rep(j, 1, n) {
                if (s[j - 1] == '.' && s[j] == '#') swap(t[j], t[j - 1]);
            }
            s = move(t);
            if (s.find('#') == string::npos) {
                ans = i + 1;
                break;
            }
        }
        return ans;
    };
    dump(native(s, n));

    int ans = 0;
    int idx = 0, len = 0;
    rep(i, 0, n) {
        if (s[i] == '#') {
            if (idx + len * 2 > i) {
                len++;
            } else {
                len = 1;
                idx = i;
            }
            chmax(ans, idx + 2 * len - 1);
        }
    }
    print(ans);

    return 0;
}