#include <stdio.h>
#define MAX 201719

int tab[MAX] = {};

inline int max(int a, int b){
	if(a > b){return a;}

	return b;
}
int main(){
	int n, i, a, maximum = -1, value = -1;
	scanf("%d", &n);
	for(i = n; i > 0; --i){
		scanf("%d", &a);
		maximum = max(maximum, a);
		tab[a]++; 
	}
	value = maximum;
	for(i = 0; i < maximum; i++){
		tab[i+1] += tab[i] >> 1;
		
	}
	i = maximum;
	while(tab[i] != 0){
		tab[i+1] += tab[i] >> 1;
		if(tab[i+1] == 0) { break;}
		i++;
	}
	printf("%d", i);
	return 0;
}