#include <bits/stdc++.h>

#define REP(i,n) for(int i=0;i<(int)(n);i++)
#define ALL(x) (x).begin(),(x).end()

using namespace std;

typedef long long ll;

const int SIZE = 2048;
const int dx[4] = {1, 0, -1, 0};
const int dy[4] = {0, 1, 0, -1};

bool p[SIZE];

bool dfs(int y, int x, int t, int w, vector<bool> &visited) {
  if (y < 0 || x < 0 || x >= w) return false;
  int n = y * w + x + 1;
  if (n > t) return false;
  if (n == t) return true;
  if (p[n]) return false;
  if (visited[n]) return false;
  visited[n] = true;
  REP(dir,4)
    if (dfs(y + dy[dir], x + dx[dir], t, w, visited))
      return true;
  return false;
}

int solve(string str) {
  if (str.size() >= 8) return 8;
  int N = stoi(str);
  for (int i = 1; i < N; ++i) {
    vector<bool> visited(N+1, false);
    if (dfs(0, 0, N, i, visited)) return i;
  }
  return -1;
}

int main() {
  for (int i = 2; i < SIZE; ++i) p[i] = true;
  for (int i = 2; i*i <= SIZE; ++i)
    if (p[i])
      for (int j = i*i; j <= SIZE; j += i)
        p[j] = false;
  string str;
  cin >> str;
  cout << solve(str) << endl;
  return 0;
}