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#include <cstdio>
#include <cstring>

int cnt[210001];

int main() {
	int N;
	int res=0;
	memset(cnt,0,sizeof(cnt));
	scanf("%d",&N);

	for (int i=0; i<N; ++i) {
		int a;
		scanf("%d",&a);
		cnt[a]++;
	}

	for (int i=0; i<210000; ++i) {
		cnt[i+1] += cnt[i]/2;
		if (cnt[i]>0) res=i;
	}

	printf("%d\n",res);

	return 0;
}