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#include <bits/stdc++.h>
using namespace std;
#define sz(x) (int)(x).size()
#define all(x) (x).begin(), (x).end()
#define st first
#define nd second
#define pb push_back
#define REP(i,a,b) for(int i = (a); i <= (b); i++)
#define FOR(i, n) REP(i, 0, int(n) - 1)
#define pii pair < int, int >
#define ll long long
#define fi first
#define se second
#define mp make_pair
#define vi vector <int>

const int MAXN = 1000;

int tab[1000000];

void add(int a) {
    while(tab[a] == 1) {
        tab[a] = 0;
        a++;
    }
    tab[a] = 1;
}

int main() {
    ios_base::sync_with_stdio(0);
    /*REP(i,1,MAXN-1) dp[i][0] = 1;
    FOR(i,MAXN) dp[0][i] = 0;
    REP(n,1,MAXN-1) {
        REP(t,1,MAXN-1) {
            for(int j=max(0,t-n+1); j<=t; j++) dp[n][t] += dp[n-1][j];
            if( (n%4 <=1) &&  t == n*(n-1)/4 )cout<<n<<" "<<t<<" "<<dp[n][t]<<" "<<dp[n][t] - 1000000000000000000LL<<"\n";
        }
    }*/
    int n;
    cin>>n;
    FOR(i,n) {
        int a;
        cin>>a;
        add(a);
    }
    for(int i=1000000; i>=0; i--) {
        if(tab[i] == 1) {
            cout<<i<<"\n";
            return 0;
        }
    }
    return 0;
}