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#include<cstdio>
int tab[202001];
int main(){
	int n;
	scanf("%d", &n);
	int pom;
	for (int i=0; i<n; i++){
		scanf("%d", &pom);
		tab[pom]++;
	}
	int last=0;
	for (int i=0; i<202000; i++){
		tab[i+1]+=tab[i]/2;
		if (tab[i]==1)
			last=i;
	}
	printf("%d", last);
}