a = int(input())

def f(a):
  for i in range(2, 101):
    temp = a
    s = ""

    for j in range(101):

      if temp // i == 0:
        s += str(temp % i)
        if s[::-1] == '17':
          return i
        else:
          break
      else:
        s += str(temp % i)
        temp = temp // i
  
  return -1
  
print(f(a))