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

int main() {
	int n; cin >> n;
	vector<int> a;
	int pre = 0, cnt = 1; cin >> pre;
	for(int i = 0; i < n - 1; ++i) {
		int aa; cin >> aa;
		if(pre != aa) {
			a.push_back(cnt);
			cnt = 1;
			pre = aa;
		} else {
			cnt++;
		}
	}
	a.push_back(cnt);
	for(int i : a) {
		cerr << i << endl;
	}
	int nn = a.size();
	int dp[nn + 1] = {};
	int maxi = 0;
	for(int i = 1; i <= nn; ++i) {
		dp[i] = maxi + a[i - 1];
		dp[i] = max(dp[i], dp[i - 1] + a[i] - 1);
		// cout << dp[i] << endl;
		if(i - 1 >= 0) maxi = max(maxi, dp[i - 1]);
	}
	cout << dp[nn] << '\n';
	return 0;
}