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#include <bits/stdc++.h>

using namespace std;

typedef long long LL;

int cnt[201730];

int main()
{
    int n; scanf("%d", &n);
    for(int i = 1; i <= n; i++)
    {
        int x; scanf("%d", &x);
        cnt[x] ++;
    }
    int mx = 0, g = 0;
    while(1)
    {
        if(g > 201718 && cnt[g] == 0) break;
        if(cnt[g] != 0) mx = max(mx, g);
        cnt[g + 1] += cnt[g] / 2;
        g++;
    }
    printf("%d\n", mx);
    return 0;
}