#include <bits/stdc++.h>
using namespace std;
const int INF = 1000000000;
const long long LINF = 1e17;
const double PI = 3.141592653589793238;
const int mod = 1000000007;
const double eps = 0.000001;
template <typename T, typename TT>
ostream &operator<<(ostream &s, pair<T, TT> t) {
  return s << "(" << t.first << "," << t.second << ")";
}
template <typename T>
ostream &operator<<(ostream &s, vector<T> t) {
  for (int i = 0; i < (t).size(); i++)
    s << t[i] << ((i < (t).size() - 1) ? " " : "");
  return s;
}
template <typename T>
ostream &operator<<(ostream &s, set<T> t) {
  for (T x : t) s << x << " ";
  return s;
}
template <typename T>
istream &operator>>(istream &s, vector<T> &t) {
  for (int _i = 0; _i < t.size(); _i++) s >> t[_i];
  return s;
}
int isprime(int n) {
  if (n == 1) return 0;
  if (n == 2) return 1;
  for (int i = 2; i * i <= n; i++) {
    if (n % i == 0) return 0;
  }
  return 1;
}
int main(int argc, const char *argv[]) {
  int n;
  cin >> n;
  for (int m = (1); m < (1000); m++) {
    if (!isprime(n * m + 1)) {
      cout << m << "\n";
      break;
    }
  }
}
