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#include <stdio.h>

int main(void)
{
    int n, ai, ans;
    int tab[1000001] = {0};
    
    scanf("%d", &n);
    for (int i = 0; i < n; i++)
    {
        scanf("%d", &ai);
        tab[ai]++;
    }
    for (int i = 0; i < 1000000; i++)
    {
        if (tab[i] > 0) ans = i;
        tab[i+1] += tab[i] / 2;
    }
    printf("%d\n", ans);
    
    return 0;
}