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#include <iostream>
using namespace std;
const int size = 201719;
int potegi[size];


int main() {
    long n;
    cin>>n;
    int tmp;
    for(int i=0; i<n ; ++i) {
        cin>>tmp;
        potegi[tmp]++;
    }
    int k=0;
    for(int i=0; i<size-1; ++i) {
        potegi[i+1]+= potegi[i]/2;
        if(potegi[i+1] != 0) k = i+1;
    }
    int ab=k;
    while(potegi[k]/2 > 0) {
        ab++;
        k/=2;
    }
    cout<<ab<<"\n";
    return 0;
}