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#include <bits/stdc++.h>

const int MAXN = 300000;
int n, coin, a[MAXN + 2], max_nom;

int main() {
	scanf("%d", &n);
	
	for (int i = 1; i <= n; i++) {
		scanf("%d", &coin);
		a[coin]++;
	}
	
	for (int i = 0; i <= MAXN; i++) {
		a[i + 1] += a[i] / 2;
		if (a[i] > 0)
			max_nom = i;
	}
	
	printf("%d", max_nom);
	return 0;
}