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#include<bits/stdc++.h>

using namespace std;

bitset<1000009> dead;

int main()
{
    int n;
    scanf("%d",&n);
    for(int i=0;i<n;i++)
    {
        int tmp;
        scanf("%d",&tmp);
        while(dead[tmp])
            dead[tmp++] = 0;
        dead[tmp] = 1;
    }
    for(int i=1000000;i>=0;i--)
    {
        if(dead[i])
        {
            printf("%d\n",i);
            return 0;
        }
    }
}