#include <bits/stdc++.h>

int ri() {
	int n;
	scanf("%d", &n);
	return n;
}

int main() {
	int n = ri();
	int a[n + 1];
	for (int i = 0; i < n; i++) a[i] = ri();
	a[n] = -1;
	std::vector<int> b;
	int last = 0;
	for (int i = 1; i <= n; i++) {
		if (a[i - 1] != a[i]) b.push_back(i - last), last = i;
	}
	n = b.size();
	int dp[n + 1];
	memset(dp, 0, sizeof(dp));
	for (int i = 0; i < n; i++) {
		// no use
		dp[i + 1] = std::max(dp[i + 1], dp[i]);
		// use
		dp[std::min(i + 2, n)] = std::max(dp[std::min(i + 2, n)], dp[i] + b[i]);
	}
	std::cout << dp[n] << std::endl;
	return 0;
}