import std.conv, std.stdio, std.string;
import std.algorithm, std.array, std.bigint, std.container, std.math, std.range, std.regex, std.typecons;
import core.bitop;

class EOFException : Throwable { this() { super("EOF"); } }
string[] tokens;
string readToken() { for (; tokens.empty; ) { if (stdin.eof) { throw new EOFException; } tokens = readln.split; } auto token = tokens.front; tokens.popFront; return token; }
int readInt() { return readToken().to!int; }
long readLong() { return readToken().to!long; }
real readReal() { return readToken().to!real; }

void chmin(T)(ref T t, in T f) { if (t > f) t = f; }
void chmax(T)(ref T t, in T f) { if (t < f) t = f; }

int binarySearch(T)(in T[] as, in bool delegate(T) test) { int low = -1, upp = cast(int)(as.length); for (; low + 1 < upp; ) { int mid = (low + upp) >> 1; (test(as[mid]) ? low : upp) = mid; } return upp; }
int lowerBound(T)(in T[] as, in T val) { return as.binarySearch((T a) => (a < val)); }
int upperBound(T)(in T[] as, in T val) { return as.binarySearch((T a) => (a <= val)); }

immutable LIM = 10^^6;
bool[] isnp;

void prepare() {
  isnp = new bool[LIM];
  isnp[0] = isnp[1] = true;
  foreach (i; 2 .. LIM) {
    if (!isnp[i]) {
      for (int j = 2 * i; j < LIM; j += i) {
        isnp[j] = true;
      }
    }
  }
}

bool[][] doIt(int H, int W, int N) {
  auto A = new bool[][](H, W);
  foreach (x; 0 .. H) foreach (y; 0 .. W) {
    A[x][y] = (1 + x * W + y <= N) && isnp[1 + x * W + y];
  }
  auto vis = new bool[][](H, W);
  void dfs(int x, int y) {
    vis[x][y] = true;
    foreach (dir; 0 .. 4) {
      const xx = x + [+1, 0, -1, 0][dir];
      const yy = y + [0, +1, 0, -1][dir];
      if (0 <= xx && xx < H && 0 <= yy && yy < W && A[xx][yy]) {
        if (!vis[xx][yy]) {
          dfs(xx, yy);
        }
      }
    }
  }
  dfs(0, 0);
  return vis;
}

int solveSmall(int N) {
  foreach (W; 1 .. N) {
    const H = (N + W + 1) / W;
    const vis = doIt(H, W, N);
    if (vis[(N - 1) / W][(N - 1) % W]) {
      return W;
    }
  }
  return -1;
}

bool isPrime(BigInt n) {
  if (n <= 1 || n % 2 == 0) return (n == 2);
  BigInt power(BigInt a, BigInt e, BigInt m) {
    BigInt x = a, y = 1;
    for (; e != 0; e >>= 1, x = x * x % m) if (e & 1) y = y * x % m;
    return y;
  }
  BigInt d;
  int r, s;
  for (d = n - 1, s = 0; d % 2 == 0; d >>= 1, ++s) {}
  foreach (a; 2 .. 100) if (a < n) {
    BigInt ad = power(BigInt(a), d, n);
    if (ad == 1) continue;
    for (r = 0; r < s; ++r) {
      if (ad == n - 1) break;
      ad = ad * ad % n;
    }
    if (r == s) return false;
  }
  return true;
}

void main() {
  prepare();
  
  /*
  foreach (W; 1 .. 30) {
    const vis = doIt(2 * W, W, 2 * W * W);
    foreach (x; 0 .. 2 * W) {
      foreach (y; 0 .. W) {
        writef("%s%4s%s", vis[x][y] ? "[" : " ", 1 + x * W + y, vis[x][y] ? "]" : " ");
      }
      writeln();
    }
    writeln();
  }
  return;
  */
  
  try {
    for (; ; ) {
      const N = readToken().to!BigInt;
      int ans;
      if (N <= 20 * 20) {
        ans = solveSmall(cast(int)(N));
      } else {
        foreach (W; [8, 14, 17, 19, 20]) {
          auto vis = new bool[W^^2];
          bool ok;
          void dfs(BigInt n) {
            if (n <= N && !isPrime(n)) {
              if (N - n >= W^^2) {
                ok = true;
                return;
              }
              if (!vis[cast(int)(N - n)]) {
                vis[cast(int)(N - n)] = true;
                const y = cast(int)((n - 1) % W);
                dfs(n - W);
                dfs(n + W);
                if (0 <= y - 1) {
                  dfs(n - 1);
                }
                if (y + 1 < W) {
                  dfs(n + 1);
                }
              }
            }
          }
          dfs(N);
          if (ok) {
            ans = W;
            break;
          }
        }
      }
      writeln(ans);
    }
  } catch (EOFException e) {
  }
}