#include "bits/stdc++.h"

#pragma GCC optimize("Ofast")
#pragma GCC targetr("avx2")

using namespace std;

using ll = long long;
using LL = long long;
using pii = pair<int, int>;

LL n;
LL a[100005];
LL dp[100005][65];
LL par[100005][65];

void solve(int TC) {
	cin >> n;
	for (int i = 1; i <= n; i++) {
		cin >> a[i];
	}
	for (int i = 0; i <= 61; i++) {
		dp[1][i] = 1;
		par[1][i] = 1;
	}
	for (int i = 2; i <= n; i++) {
		LL gap = a[i] - a[i - 1] - 1;
		LL lay = 0;
		LL one = 1;
		while (gap >= one) {
			lay++;
			gap -= one;
			one *= 2;
		}
		dp[i][0] = dp[i - 1][0] + 1;
		for (int j = 1; j <= 61; j++) {
			if (j > lay + 1) {
				dp[i][j] = par[i - 1][j];
			}
			else if (j == lay + 1) {
				if (!gap) dp[i][j] = par[i - 1][j];
				else {
					LL take = max(gap + 1, one / 2 + 1);
					dp[i][j] = par[i - 1][j - 1] + take;
					dp[i][j] = max(dp[i][j], dp[i - 1][j] + gap);
				}
			}
			else {
				dp[i][j] = dp[i - 1][j] + (1 << (j - 1));
			}
		}
		par[i][0] = dp[i][0];
		for (int j = 1; j <= 61; j++) {
			par[i][j] = max(par[i][j - 1], dp[i][j]);
		}
	}
	LL mx = 0;
	for (int i = 0; i <= 61; i++) {
		mx = max(mx, dp[n][i]);
	}
	cout << mx << "\n";
	return;
}

int32_t main() {
	cin.tie(0)->sync_with_stdio(0);
	cout << fixed << setprecision(10);

	int t = 1;
	// cin >> t;
	for (int i = 1; i <= t; i++) {
		solve(i);
	}
}