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#include <cstdio>
#include <cstring>

const int cs = 234567;
int c[cs];

int main(int argc, char** argv) {
  int n;
  scanf("%d",&n);
  int* a = new int[n];
  for(int i=0;i<n;i++) {
    scanf("%d",&a[i]);
  }

  memset(c, 0, sizeof(c));

  for(int i=0;i<n;i++) {
    c[a[i]]++;
  }

  for(int i=0;i<cs-1;i++) {
    if(c[i] > 1) {
      c[i+1] += c[i]/2;
    }
  }

  int res = 0;
  for(int i=cs-1;i>=0;i--) {
    if(c[i] > 0) {
      res = i;
      break;
    }
  }

  printf("%d\n", res);
  return 0;
}