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/*
wynik = najstarszy bit sumy potęg dwójki 

limity:
0<=a<=201718<2^18
1<=n<=1e6<2^20
*/

#include <stdio.h>
#include <string.h>

char s[201800];

int main()
{
  int n, a, x=0;

  bzero(s, sizeof(s));
  scanf("%d", &n);
  while (n--)
  {
    scanf("%d", &a);
    while (s[a] == 1) s[a++] = 0;
    s[a] = 1;
    if (x<a) x = a;
  }
  printf("%d\n", x);
  return 0;
}