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#include <iostream>

using namespace std;

int main()
{
    int n, a, tabSize = 201718 + 25;
    int tab[tabSize];
    cin>>n;
    for(int i=0; i < tabSize; i++) {
        tab[i] = 0;
    }
    for(int i=0; i < n; i++) {
        cin>>a;
        tab[a]++;
    }
    for(int i=0; i < tabSize; i++) {
        if (tab[i] > 1) {
            bool odd = tab[i] % 2 == 1 ? true : false;
            tab[i] /= 2;
            int j = 1;
            while(tab[i] > 0) {
                if (tab[i] % 2 == 1) {
                    tab[i + j]++;
                }
                j++;
                tab[i] /= 2;
            }
            if (odd) {
                tab[i] = 1;
            }
        }
    }
    int max = 0;
    for (int i = tabSize - 1; i >= 0; i--){
        if (tab[i] == 1) {
            cout<<i<<endl;
            break;
        }
    }
    

    return 0;
}