#include <bits/stdc++.h>
using namespace std;
const int dx[] = {1, 0, -1, 0, 1, 1, -1, -1};
const int dy[] = {0, 1, 0, -1, -1, 1, 1, -1};
const double EPS = 1e-6;
const int INF = 0x3f3f3f3f;
inline int sign(const double &x) {
  if (fabs(x) < EPS) {
    return 0;
  } else {
    return x < 0 ? -1 : 1;
  }
}
int mian();
int main() {
  mian();
  return 0;
}
int gcd(int x, int y) {
  if (!x || !y) {
    return x > y ? x : y;
  }
  for (int t; (t = (x % y)); x = y, y = t)
    ;
  return y;
}
int tab[1111000] = {1, 1, 0};
int mian() {
  for (int i = 2; i < 1000000; ++i) {
    if (tab[i]) continue;
    for (int j = i + i; j <= 1000000; j += i) {
      tab[j] = 1;
    }
  }
  int n, m;
  while (scanf("%d", &n) != EOF) {
    for (int i = 1; i <= 1000; ++i) {
      if (tab[n * i + 1]) {
        printf("%d\n", i);
        break;
      }
    }
  }
  return 0;
}
