#include <algorithm>
#include <array>
#include <bitset>
#include <cassert>
#include <chrono>
#include <cmath>
#include <cstdint>
#include <cstring>
#include <functional>
#include <iomanip>
#include <iostream>
#include <map>
#include <numeric>
#include <queue>
#include <random>
#include <set>
#include <vector>
#include <climits>
using namespace std;
#define endl '\n'
#define all(x) begin(x), end(x)

void dbg_print(int x) {cerr << x;}
void dbg_print(long x) {cerr << x;}
void dbg_print(long long x) {cerr << x;}
void dbg_print(unsigned x) {cerr << x;}
void dbg_print(unsigned long x) {cerr << x;}
void dbg_print(unsigned long long x) {cerr << x;}
void dbg_print(float x) {cerr << x;}
void dbg_print(double x) {cerr << x;}
void dbg_print(long double x) {cerr << x;}
void dbg_print(char x) {cerr << '\'' << x << '\'';}
void dbg_print(const char *x) {cerr << '\"' << x << '\"';}
void dbg_print(const string &x) {cerr << '\"' << x << '\"';}
void dbg_print(bool x) {cerr << (x ? "true" : "false");}
template<typename T, typename V>
void dbg_print(const pair<T, V> &x) {cerr << '{'; dbg_print(x.first); cerr << ','; dbg_print(x.second); cerr << '}';}
template<typename T>
void dbg_print(const T &x) {int f = 0; cerr << '{'; for (auto &i: x) cerr << (f++ ? "," : ""), dbg_print(i); cerr << "}";}
void _print() {cerr << "]\n";}
template <typename T, typename... V>
void _print(T t, V... v) {dbg_print(t); if (sizeof...(v)) cerr << ", "; _print(v...);}
template<size_t T>
void dbg_print(bitset<T> b) {cerr << b;}
#ifndef ONLINE_JUDGE
#define debug(x...) cerr << "[" << #x << "] = ["; _print(x)
#else
#define debug(x...)
#endif

// ============================================================================================== //

typedef long long ll;

struct base {
double a, b;
base(double _a = 0, double _b = 0) : a(_a), b(_b) { }
const base operator+(const base &c) const { return base(a + c.a, b + c.b); }
const base operator-(const base &c) const { return base(a - c.a, b - c.b); }
const base operator*(const base &c) const {
return base(a * c.a - b * c.b, a * c.b + b * c.a);
}
};

const double PI = acos(-1);

void fft(vector<base> &a, bool inv = 0) {
int n = (int)a.size();

for (int i = 0; i < n; i++) {
int bit = n >> 1, j = 0, k = i;
while (bit > 0) {
if (k & 1) j += bit;
k >>= 1, bit >>= 1;
}
if (i < j) swap(a[i], a[j]);
}

double angle = 2 * PI / n * (inv ? -1 : 1);
vector<base> wn(n / 2);
for (int i = 0; i < n / 2; i++) wn[i] = {cos(angle * i), sin(angle * i)};

for (int len = 2; len <= n; len <<= 1) {
int aux = len / 2;
int step = n / len;
for (int i = 0; i < n; i += len) {
for (int j = 0; j < aux; j++) {
base v = a[i + j + aux] * wn[step * j];
a[i + j + aux] = a[i + j] - v;
a[i + j] = a[i + j] + v;
}
}
}

for (int i = 0; inv && i < n; i++) a[i].a /= n, a[i].b /= n;
}

vector<int> multiply(vector<int> &ta, vector<int> &tb) {
int n = (int)ta.size(), m = (int)tb.size();
int t = n + m - 1, sz = 1;
while (sz < t) sz <<= 1;

vector<base> a(sz), b(sz), c(sz);

for (int i = 0; i < sz; i++) {
a[i] = i < n ? base((double)ta[i]) : base(0);
b[i] = i < m ? base((double)tb[i]) : base(0);
}

fft(a, 0), fft(b, 0);
for (int i = 0; i < sz; i++) c[i] = a[i] * b[i];
fft(c, 1);

vector<int> res(sz);
for (int i = 0; i < sz; i++) res[i] = int(round(c[i].a));

while ((int)res.size() > t && res.back() == 0) res.pop_back();

return res;
}

const int maxn = 1e6 + 1000;
int spf[2*maxn];
vector<int> primes;

int main() {
ios_base::sync_with_stdio(0);
cin.tie(0);

for (int i = 2; i < 2*maxn; i++) {
if (spf[i] == 0) {
primes.emplace_back(i);
spf[i] = i;
}
for (int p : primes) {
if (i * p >= 2*maxn || p > i) break;
spf[i * p] = p;
}
}

int n; cin >> n;
vector<int> freq_even(maxn / 2 + 1), freq_odd(maxn / 2 + 1);
int cnt_1 = 0;
for (int i = 0; i < n; i++) {
int c; cin >> c;
cnt_1 += c == 1;
if (c&1) freq_odd[c / 2] = 1;
else freq_even[(c - 1) / 2] = 1;
}

if (cnt_1 <= 1) cout << 2 << endl;
else {
auto ret = multiply(freq_even, freq_odd);
for (int i = 0; i < ret.size(); i++) {
if (ret[i] == 0 && spf[2*(i + 1) + 1] == 2*(i + 1) + 1) {
cout << 2*(i + 1) + 1 << endl;
break;
}
}
}
}