#include "bits/stdc++.h"
using namespace std;
#ifdef _DEBUG
#include "dump.hpp"
#include <boost/multiprecision/cpp_int.hpp>
namespace mp = boost::multiprecision;
using Int = mp::cpp_int;
#else
#define dump(...)
using Int = __int128;
#endif


#define int long long
#define rep(i,a,b) for(int i=(a);i<(b);i++)
#define rrep(i,a,b) for(int i=(b)-1;i>=(a);i--)
#define all(c) begin(c),end(c)
const int INF = sizeof(int) == sizeof(long long) ? 0x3f3f3f3f3f3f3f3fLL : 0x3f3f3f3f;
const int MOD = 1'000'000'007;
template<class T> bool chmax(T &a, const T &b) { if (a < b) { a = b; return true; } return false; }
template<class T> bool chmin(T &a, const T &b) { if (b < a) { a = b; return true; } return false; }


// エラトステネスの篩
vector<char> eratos(int n) {
	vector<char> is_prime(n + 1, true);
	is_prime[0] = is_prime[1] = false;
	for (int i = 2; i*i <= n; i++)
		if (is_prime[i]) {
			int j = i + i;
			while (j <= n) {
				is_prime[j] = false;
				j += i;
			}
		}
	return is_prime;
}

// (a*b) % mod 
template<typename Int>
Int modmul(Int a, Int b, Int mod) {
	Int x = 0, y = a % mod;
	while (b > 0) {
		if (b & 1)x = x + y % mod;
		y = y * 2 % mod;
		b >>= 1;
	}
	return x % mod;
}

// mod^2 が long long の最大値より大きければオーバーフローするので掛け算に modmul を使う
template<typename Int>
Int modpow(Int a, Int e, Int mod) {
	Int res = 1;
	while (e > 0) {
		if (e & 1)res = modmul(res, a, mod);
		a = modmul(a, a, mod);
		e >>= 1;
	}
	return res;
}

// 素数判定（Miller-Rabin primality test）
// 2^24程度から
// long long で2^32以上を判定する場合は modpow で modmul を使う
// millerRabinPrimalityTest(n, 5)
template<typename Int>
bool millerRabinPrimalityTest(Int x, int iteration) {
	if (x < 2)return false;
	if (x != 2 && x % 2 == 0)return false;
	Int s = x - 1;
	while (s % 2 == 0)s /= 2;
	for (int i = 0; i < iteration; i++) {
		Int a = rand() % (x - 1) + 1, tmp = s;
		Int mod = modpow(a, tmp, x);
		while (tmp != x - 1 && mod != 1 && mod != x - 1) {
			mod = modmul(mod, mod, x);
			tmp *= 2;
		}
		if (mod != x - 1 && tmp % 2 == 0)return false;
	}
	return true;
}

signed main() {
	cin.tie(0);
	ios::sync_with_stdio(false);
	int N; cin >> N;
	if (N < 50) {
		auto e = eratos(N);
		static const int di[] = { 1,0,-1,0 };
		static const int dj[] = { 0,1,0,-1 };
		using State = tuple<int, int, int>;
		rep(w, 1, N + 1) {
			dump(w);
			vector<bool> f(N + 1);
			int H = (N - 1) / w + 1, W = w;
			auto inrange = [&](int i, int j) { return i >= 0 && i < H && j >= 0 && j < W; };
			auto bfs = [&](int si, int sj, int gi, int gj) {
				queue<State> q;
				q.emplace(0, si, sj);
				while (q.size()) {
					int d, ci, cj; tie(d, ci, cj) = q.front(); q.pop();
					if (ci == gi && cj == gj)return d;
					rep(i, 0, 4) {
						int ni = ci + di[i], nj = cj + dj[i];
						int nx = ni * w + nj + 1;
						if (!inrange(ni, nj))continue;
						if (nx > N)continue;
						if (e[nx])continue;
						if (f[nx])continue;
						f[nx] = true;
						q.emplace(d + 1, ni, nj);
					}
				}
				return -1LL;
			};
			auto res = bfs(0, 0, (N - 1) / w, (N - 1) % w);
			dump(res);
			if (res != -1) {
				cout << w << endl;
				break;
			}
		}
	}
	else {
		for (int w = 8;; w += 2) {
			if (millerRabinPrimalityTest(Int(1 + w), 5))continue;
			if (((N - 1) % w) == 0 && millerRabinPrimalityTest(Int(N - w), 5))continue;
			cout << w << endl;
			break;
		}
	}
	return 0;
}