#include <iostream>
#include <algorithm>
#include <cmath>
#include <vector>
#include <complex>
#include <queue>
#include <deque>
#include <set>
#include <map>
#include <unordered_set>
#include <unordered_map>
#include <iomanip>
#include <assert.h>
#include <array>
#include <cstdio>
#include <cstring>
#include <random>
#include <functional>
#include <numeric>
#include <bitset>

using namespace std;

#define REP(i,a,b) for(int i=a;i<(int)b;i++)
#define rep(i,n) REP(i,0,n)
#define all(c) (c).begin(), (c).end()
#define zero(a) memset(a, 0, sizeof a)
#define minus(a) memset(a, -1, sizeof a)
#define minimize(a, x) a = std::min(a, x)
#define maximize(a, x) a = std::max(a, x)

typedef long long ll;
int const inf = 1<<29;

typedef __int128_t INT;

INT N;

INT pow(INT x, INT n, INT M){
  INT tmp = 1;

  if ( n > 0 ){
    tmp = pow(x, n/2, M);
    if ( n%2 == 0 ) tmp = (tmp*tmp)%M;
    else tmp = (((tmp*tmp)%M)*x)%M;
  }
  return tmp;
}

bool is_prime(INT const& x) {
  if(x == 2) { return 1; }
  if(x < 2 || (x%2 == 0)) { return 0; }
  return pow(2, x-1, x) == 1;
}

bool dfs(INT n, int cnt) {

  if(N - n > 10) {
    return true;
  }

  bool ret = false;

  if(!is_prime(n-1)) {
    ret = ret || dfs(n-1, cnt);
  }
  if(!is_prime(n-cnt)) {
    ret = ret || dfs(n-cnt, n-cnt);
  }
  
  return ret;
}

int main() {

  string s; cin >> s;
  N = 0;
  rep(i, s.size()) {
    N *= 10; N += s[i]-'0';
  }

  if(N < 7) {
    cout << (int)N-1 << endl; exit(0);
  }

  int cnt = 7;
  while(1) {
    bool r = dfs(N, cnt);
    if(r) {
      cout << cnt << endl;
      exit(0);
    }
    cnt++;
  }
  
  return 0;
}