import sys
read = sys.stdin.buffer.read
readline = sys.stdin.buffer.readline
readlines = sys.stdin.buffer.readlines
sys.setrecursionlimit(10 ** 7)


def Base_10_to_n(x, n):
    if int(x / n):
        return Base_10_to_n(int(x / n), n) + str(x % n)
    return str(x % n)


a = int(readline())
for x in range(2, 10 ** 4):
    if Base_10_to_n(a, x) == '17':
        print(x)
        break
else:
    print(-1)