require 'prime'

N_MAX = 110
$mp = Array.new(N_MAX).map{Array.new(N_MAX,0)}
$used = Array.new(N_MAX).map{Array.new(N_MAX,false)}
$n = gets.chomp.to_i

$vx = [1,0,-1,0]
$vy = [0,1,0,-1]
def dfs(w,h,y,x)
  return false if y<0 || x<0 || y>=h || x>=w
  return false if $used[y][x]
  $used[y][x] = true
  return false if $mp[y][x]==1e9
  return true if $mp[y][x]==$n
  t = $mp[y][x]
  return false if isP_MR(t)
  for i in 0...4
    return true if dfs(w,h,y+$vy[i],x+$vx[i])
  end
  return false
end

def powmod(a,b,m)
  result = 1
  while b>0
    result = (result*a)%m if b&1==1
    a = (a*a)%m
    b >>= 1
  end
  return result
end

# https://ja.wikipedia.org/wiki/%E3%83%9F%E3%83%A9%E3%83%BC%E2%80%93%E3%83%A9%E3%83%93%E3%83%B3%E7%B4%A0%E6%95%B0%E5%88%A4%E5%AE%9A%E6%B3%95
def isP_MR(q)
  k = 1000
  # return Prime.prime?(q) if q<10000000
  return true if q==2
  return false if q<2
  return false if q&1==0

  d = q-1
  while d&1==0
    d>>=1
  end
  # r = [q-1,(2*Math.log(q)**2).floor].min
  for i in 0...k
    a = rand(q-2)+1
    t = d
    y = powmod(a,t,q)
    while t!=q-1 && y!=1 && y!=q-1
      y = (y*y) % q
      t <<= 1
    end
    if y!=q-1 && t&1==0
      return false
    end
  end
  return true
end

if $n<100
  for w in 3...$n
    h = $n/w + ( $n%w == 0 ? 0 : 1 )
    for i in 0...N_MAX
      for j in 0...N_MAX
        $mp[i][j] = 1e9
        if i<h && j<w && i*w+j<$n
          $mp[i][j] = i*w+j+1
        end
        $used[i][j] = false
      end
    end
    if dfs(w,h,0,0)
      puts w
      break
    end
  end
else
  c = 8
  while true
    # process
    if $n%c!=1
      puts c
      break
    end
    if isP_MR($n-c)
      puts c
      break
    end
    # succeed
    while true
      c += 2
      break if !isP_MR(c+1)
    end
  end
end