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#include<stdio.h>

int counters[210009];

int main() {

  int n, a;
  int max = 0;
  
  scanf("%d", &n);
  while(n--) {
    scanf("%d", &a);
    counters[a]++;
  }
  
  for(int i = 0; i < 210000; i++) {
    int modulo = counters[i] % 2;
    counters[i + 1] += counters[i] / 2;
    counters[i] = modulo;
    if(modulo == 1) {
      max = i;
    }
  }
  
  printf("%d", max);

}