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#include <bits/stdc++.h>
using namespace std;
int a, b, c, n, d, tab[1000001], w;
int main () {
	cin >> n;
	for (int i = 0; i < n; i++) {
		cin >> a;
		tab[a]++;
	}
	for (int i = 0; i < 1000000; i++) {
		d = tab[i]/2;
		tab[i+1] += d;
		if (tab[i] != 0) w = i;
	}
	cout << w << endl;
}