#include<iostream>

using namespace std;

int main() {
	int n;
	const int M = 201740;
	bool* values = new bool[M];
	for (int i = 0; i < M; i++)values[i] = false;
	cin >> n;
	int m = 0;
	while (n > 0) {
		int a;
		cin >> a;
		for (int i = 0; i < M - a; i++) {

			if (values[a+i]) {
				values[a +i+ 1];
				values[a+i] = false;
			}
			else {
				values[a + i] = true;
				if (a + i > m) m = a + i;
                                break;
			}
		}
		n--;
	}	
	cout << m;
	return 0;
}