#include <iostream>
#include <string>
#include <cstdlib>
#include <queue>
#include <cassert>
using namespace std;

int main(){
	const int M = 200;
	
	int dd[] = {0, -1, 0, 1, 0};

	bool npr[M + 1] = {true, true};
	for(int i = 2; i <= M; ++i){
		if(!npr[i]){
			for(int j = i * 2; j <= M; j += i){
				npr[j] = true;
			}
		}
	}
	
	string s;
	cin >> s;
	int n;
	if(s.size() > 2){
		n = 50;
	}
	else{
		n = strtol(s.c_str(), 0, 10);
	}
	if(n > 50){ n = 50; }
	
	int ans;
	for(ans = 3; ; ++ans){
		assert(ans < n);
		vector<char> vis(n + 1);
		vis[1] = 1;
		queue<int> q;
		q.push(1);
		while(!q.empty()){
			int y = (q.front() - 1) / ans;
			int x = (q.front() - 1) % ans;
			q.pop();
			for(int i = 0; i < 4; ++i){
				int ny = y + dd[i], nx = x + dd[i + 1];
				if(ny < 0 || nx < 0 || nx >= ans){ continue; }
				int t = ny * ans + nx + 1;
				if(t > n || !npr[t] || vis[t]){ continue; }
				vis[t] = 1;
				q.push(t);
			}
		}
		if(vis[n]){ break; }
	}
	cout << ans << endl;
}