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#include <cstdio>
using namespace std;

const int N = 201718 + 40;
int howMany[N + 1];

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

    int result = 0;
    for(int i = 1; i <= N; ++i) {
        howMany[i] += (howMany[i - 1] >> 1);
        if(howMany[i] != 0)
            result = i;
    }
    printf("%d", result);

    return 0;
}