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#include<bits/stdc++.h>

using namespace std;

#define MAXN 250000

int n;
int arr[MAXN];

int solve() {
	int maxi = 0;
	for(int i=0;i<MAXN-1;i++) {
		maxi = arr[i] > 0 ? i: maxi ;
		arr[i+1] += arr[i] >> 1;
	}

	return maxi;
}
int main() {
	ios_base::sync_with_stdio(0);
	cin.tie(0);
	cout.tie(0);
	cin >> n;
	for(int i=0;i<n;i++) {
		int tmp;
		cin >> tmp;
		arr[tmp]++;
	}
	
	cout << solve() << "\n";
	return 0;
}