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#include<bits/stdc++.h>

using namespace std;

int ans = 0, N, M, ap[222000];

int main ()
{
scanf ("%d", &N);
for (int i=1; i<=N; i++)
{
    int x;
    scanf ("%d", &x), ap[x] ++;
    if (x > M) M = x;
}
for (int i=0; i<=M || ap[i]; i++)
{
    ap[i + 1] += (ap[i] >> 1), ap[i] &= 1;
    if (ap[i]) ans = i;
}
printf ("%d\n", ans);
return 0;
}