#include <algorithm>
#include <cstdio>
#include <cstdlib>
#include <vector>
int main()
{
constexpr int max_n{ 1000000 };
constexpr int max_a{ 201718 };
int n;
std::scanf("%d", &n);
std::vector<int> a;
a.resize(n);
int actual_min_a{ max_a };
int actual_max_a{ 0 };
for (int i{ 0 }; i < n; ++i) {
std::scanf("%d", &(a[i]));
actual_min_a = std::min(actual_min_a, a[i]);
actual_max_a = std::max(actual_max_a, a[i]);
}
std::vector<int> powers;
powers.resize(actual_max_a + 1);
for (int i{ 0 }; i < n; ++i) {
++powers[a[i]];
}
int reminder{ 0 };
int final_power{ actual_min_a };
for (; final_power <= actual_max_a; ++final_power) {
reminder = (powers[final_power] + reminder) / 2;
}
while (reminder > 0) {
reminder /= 2;
++final_power;
}
--final_power;
std::printf("%d\n", final_power);
}