#include <bits/stdc++.h>
using namespace std;
using ll = long long;
ll power(const ll a, const ll n, const ll mod = -1)
{
    if (n == 0) { return 1; }
    if (n % 2 == 1) {
        return ((__int128_t)(1) * power(a, n - 1, mod) * a) % mod;
    } else {
        const ll aa = power(a, n / 2, mod);
        return ((__int128_t)(1) * aa * aa) % mod;
    }
}
bool MillerRabin(const ll n)
{
    if (n == 1) { return false; }
    constexpr int TEST = 1000;
    ll s = 0, d = n - 1;
    for (; d % 2 == 0; s++, d /= 2) {}
    static mt19937 mt{random_device{}()};
    uniform_int_distribution<ll> dist{1, n - 1};
    for (int i = 0; i < TEST; i++) {
        const ll a = dist(mt);
        if (power(a, n - 1, n) != 1) { return false; }
        ll num = power(a, d, n);
        if (num != 1) {
            for (ll r = 0; r < s; r++) {
                if (num == n - 1) { return false; }
                num = ((__int128_t)(1) * num * num) % n;
            }
        }
    }
    return true;
}
int main()
{
    ll N;
    cin >> N;
    cout << (N >= 26 ? MillerRabin(N - 8) ? 14 : 8 : N == 9 ? 7 : N == 10 ? 7 : N == 15 ? 7 : N == 16 ? 7 : N == 21 ? 19 : N == 22 ? 7 : N == 25 ? 23 : N - 1) << endl;
    return 0;
}