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#include <iostream>
using namespace std;
int kasa[1000000]={0};
int main() {
	int n,a,max_kasa=0;
	cin>>n;
	for(int i=0;i<n;i++){
		cin>>a;
		kasa[a]++;
		if(a>max_kasa)max_kasa=a;
	}
	int i=0;
	while(1)
	{
		if(kasa[i]<2&&max_kasa<=i)
		{
			cout<<i;
			break;
		}
		if(kasa[i]>=2)
		{
			kasa[i+1]+=kasa[i]/2;
			kasa[i]=kasa[i]%2;
			
		}
		i++;
		
	}
	return 0;
}