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

int ile[250000], wyn, a, n;

int main()
{
	scanf("%d", &n);
	for (int i = 1; i <= n; i++)
		scanf("%d", &a), ile[a]++;
		
	for (int i = 0; i < 250000; i++)
	{
		ile[i + 1] += (ile[i]/2);
		ile[i] -= ((ile[i]/2) * 2);
		
		if (ile[i] >= 1)
			wyn = max(wyn, i);
	}
	printf("%d", wyn);
}