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#include <iostream>

using namespace std;

const int MAX_EXPONENT = 201718 + 30;
int quantities[MAX_EXPONENT+1];


int main() {
    ios_base::sync_with_stdio(0);
    int n; cin >> n;
    
    for (int i = 0; i < n; ++i) {
        int a; cin >> a;
        quantities[a]++;
    }
    
    int biggest = 0;
    for (int i = 0; i < MAX_EXPONENT; ++i) {
        quantities[i+1] += quantities[i] / 2;
        quantities[i] %= 2;
        if (quantities[i+1] > 0)
            biggest = i+1;
    }
    
    cout << biggest << endl;
        
    return 0;
}