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#include<bits/stdc++.h>

using namespace std;

int n,a;
int bin[202000];

int main()
{
    ios_base::sync_with_stdio(0);
    cin>>n;
    for(int i = 0;i<n;i++) {
        cin>>a;
        bin[a]++;
    }
    int mx = 0, cr = 0;
    for(int i = 0; i<202000;i++) {
        cr/=2;
        cr+=bin[i];
        if(cr) {
            mx = i;
        }
    }
    cout<<mx<<"\n";
}