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)
  return 1 if b==0
  p = powmod(a,b/2,m)
  p = p*p%m
  p = p*a%m if b%2==0
  return p
end

# http://d.hatena.ne.jp/pashango_p/20090704/1246692091
def isP_MR(q)
  k = 10000
  return Prime.prime?(q) if q<10000000
  return false if q&1==0

  d = (q-1)>>1
  while d&1==0
    d>>=1
  end
  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 = powmod(y,2,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