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#include <iostream>

using namespace std;

int main()
{
	int a,b,max;
	cin>>a;
	max=0;
	int tab[403436];
	for (int i=0; i<403436; i++)
	tab[i]=0;
	for (int i=0; i<a; i++)
	{
		cin>>b;
		tab[b]++;
	}
	for (int i=0; i<a; i++)
	{
	 	if (tab[i]>1) {
	tab[i+1]=tab[i]/2;
tab[i]%=2;
		 max=i+1;
	}
	else if (tab[i]==1) max=i;
	}
	cout<<max;
}