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#include <bits/stdc++.h>

using namespace std;

int main() {
	ios_base::sync_with_stdio(0);

	int n;
	cin >> n;

	vector<int> V(500000, 0);

	int a;
	for(int i = 0; i < n; i++) {
		cin >> a;
		V[a]++;
	}

	for(int i = 0; i < V.size()-1; i++) {
		if(V[i] % 2 == 1) {
			V[i+1] += (V[i]-1)/2;
			V[i] = 1;
		} else {
			V[i+1] += V[i]/2;
			V[i] = 0;
		}
	}

	for(int i = V.size()-1; i >= 0; i--) {
		if(V[i] > 0) {
			cout << i << endl;
			return 0;
		}
	}

	return 0;
}