#include <bits/stdc++.h>
using namespace std;
#pragma comment(linker, "/stack:200000000")
#pragma GCC optimize("Ofast")
#pragma GCC target( \
    "sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,avx2,tune=native")
#pragma GCC optimize("-ffloat-store")
const long long INF = 0xFFFFFFFFFFFFFFFL;
const long long N = 1e9 + 7;
vector<long long> pri;
void yo(int n) {
  bool prime[n + 1];
  memset(prime, true, sizeof(prime));
  for (int p = 2; p * p <= n; p++) {
    if (prime[p] == true) {
      for (int i = p * p; i <= n; i += p) prime[i] = false;
    }
  }
  for (int p = 2; p <= n; p++)
    if (prime[p]) pri.push_back(p);
}
void solve() {
  long long n;
  cin >> n;
  for (long long i = 1; i < 1001; i++) {
    if (!binary_search((pri).begin(), (pri).end(), n * i + 1)) {
      cout << i;
      return;
    }
  }
}
int32_t main(int32_t argc, char **argv) {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  yo(1000003);
  long long t;
  t = 1;
  while (t--) solve();
  cerr << "\n"
       << "Time : " << 1000 * ((double)clock()) / (double)CLOCKS_PER_SEC
       << "ms\n";
  return 0;
}
