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#include <bits/stdc++.h>
#define fr(i,n) for(int i = 0 ; i < (n);i++)
using namespace std;
int m[201800];
int main ()
{
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    cout.tie(NULL);
    int n;
    cin >> n;
    fr ( i, n )
    {
        int x;
        cin >> x;
        m[x]++;
    }
    int maks=0;
    fr ( i, 201799 )
    {
        if ( m[i] )
            maks=i;
        while ( m[i] > 1 )
        {
            m[i+1]++;
            m[i]--;
            m[i]--;
        }
    }
    cout << maks;
    return 0;
}