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#include<iostream>
using namespace std;

const int N = 201718 + 19 + 7;
int A[N] = {0};

int main() {
	int n;
	cin>>n;
	for(int i=0; i<n; i++) {
		int a;
		cin>>a;
		A[a]++;
	}
	int m = 1;
	for(int i=1; i<N-1; i++) {
		if(A[i] > 0) m = i;
		A[i+1] += A[i]/2;
	}
	cout<<m<<endl;
	return 0;
}