#include "bits/stdc++.h"
using namespace std;
#define ll long long
#define endl '\n'
#define rep(i, n) for(int i = 0; i < (int)(n); i++)
#define rep2(i,a,b) for(int i=int(a);i<int(b);i++)
#define pb emplace_back
#define all(x) (x).begin(),(x).end()
int mod=1e9+7;
int mod2=998244353;
const int INF=1e9;

signed main(){
	ll n;
	cin>>n;
	vector<ll> d(n);
	rep(i,n)cin>>d[i];
	vector<ll> lis;
	rep2(i,1,min(5LL,n+1)){
		rep(j,n-(i-1)){
			ll tmp=0;
			rep(k,i){
				tmp*=10;
				tmp+=d[j+k];
			}
			lis.pb(tmp);
		}
	}

	sort(all(lis));
	unique(all(lis));
	
	rep(i,lis.size()){
		if(lis[i]!=i){
			cout<<i<<endl;
			return 0;
		}
	}
	cout<<lis.size()<<endl;
}

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