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

const long long mod = 1e9 + 7;
// const long long mod = 998244353;
const double PI = acos(-1);
using ll = long long;
using PII = pair<int, int>;
using PLL = pair<long long, long long>;
#define REP(i,n) for(int i=0, i##_len=(n); i<i##_len; ++i)
#define rrep(i,a,b) for(int i=(a);i>(b);i--)
#define rep(i,a,b) for(int i=(a);i<(b);i++)

// begin() end()
#define all(x) (x).begin(),(x).end()

//出力系
#define print(x) cout << x << endl
#define prints(x) cout << fixed << setprecision(12) << x << endl
#define printc(x) cout << setw(6) << setfill('0') << x << endl;
#define yes cout << "Yes" << endl
#define YES cout << "YES" << endl
#define no cout << "No" << endl
#define NO cout << "NO" << endl

//最大公約数 
 ll gcd(ll x, ll y) { return y ? gcd(y,x%y) : x;}
 
// 最小公倍数
unsigned lcm(unsigned a, unsigned b){
	return a / gcd(a, b) * b; 
}
const int INF = 1000000000;
const double DINF = 1LL<<60;
const long long LINF = 1LL<<60;
const int MAX = 510000;

template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }

// Nは問題によって変更すること
// vector<int>ind(N);
// REP(i, N) ind[i]= i;
//sort(all(ind), [&](int i, int j) {return x[i] < x[j];});


ll dy[4] = {0, 1, 0, -1}, dx[4] = {1, 0, -1, 0};
// ll dy[8] = {0, 1, 1, 1, 0, -1, -1, -1}, dx[8] = {1, 1, 0, -1, -1, -1, 0, 1};


vector<vector<int>>G;


int main() {
	int N;
	cin >> N;
	string S;
	cin >> S;
	ll ans = 0;
	ll cnt = 0;
	rrep(i, N - 1, -1){
		if(S[i] != '#'){
			cnt = max(0LL, cnt - 1);
			continue;
		}
		chmax(ans, (N - i) + cnt);
		cnt++;
	}

	cout << ans << endl;
	

	return 0;
}