Buggy python submission (verdict: Time Limit Exceeded):
from __future__ import print_function

import sys
sys.setrecursionlimit(500000)

import re
import array
import copy
import functools
import operator

import math
import string
import fractions
from fractions import Fraction

import collections
import itertools
import bisect

import random
import time

import heapq
from heapq import heappush
from heapq import heappop
from heapq import heappushpop
from heapq import heapify
from heapq import heapreplace
from queue import PriorityQueue as pq
from queue import Queue

from itertools import accumulate

from collections import deque
from collections import Counter

from operator import mul
from functools import reduce

input = sys.stdin.readline


def eprint(*args, **kwargs):
    print(*args, file=sys.stderr, **kwargs)
    return

# from fractions import gcd
# from math import gcd

# def lcm(n, m):
#     return int(n * m / gcd(n, m))


# def coprimize(p, q):
#     common = gcd(p, q)
#     return (p // common, q // common)


# def find_gcd(list_l):
#     x = reduce(gcd, list_l)
#     return x


def combinations_count(n, r):
    r = min(r, n - r)
    numer = reduce(mul, range(n, n - r, -1), 1)
    denom = reduce(mul, range(1, r + 1), 1)
    return numer // denom


mod=1000000007
def combinations_count_mod(n, r):
    r = min(r, n - r)
    numer = reduce(lambda x,y: x*y%mod, range(n, n - r, -1), 1)
    denom = pow( reduce(lambda x,y: x*y%mod, range(1, r + 1), 1) , mod-2, mod)
    return numer * denom % mod



def main():
    k = int(input().strip())
    if k%2==0:
        print(-1)
    else:
        temp=0
        for i in range(10**10):
            temp+=(7*(10**i)) % k
            temp=temp%k
            if temp==0:
                print(i+1)
                return



if __name__ == '__main__':
    main()

Fixed submission:
from __future__ import print_function

from functools import reduce
from operator import mul
from collections import Counter
from collections import deque
from itertools import accumulate
from queue import Queue
from queue import PriorityQueue as pq
from heapq import heapreplace
from heapq import heapify
from heapq import heappushpop
from heapq import heappop
from heapq import heappush
import heapq
import time
import random
import bisect
import itertools
import collections
from fractions import Fraction
import fractions
import string
import math
import operator
import functools
import copy
import array
import re
import sys
sys.setrecursionlimit(500000)


input = sys.stdin.readline


def eprint(*args, **kwargs):
    print(*args, file=sys.stderr, **kwargs)
    return

# from fractions import gcd
# from math import gcd

# def lcm(n, m):
#     return int(n * m / gcd(n, m))


# def coprimize(p, q):
#     common = gcd(p, q)
#     return (p // common, q // common)


# def find_gcd(list_l):
#     x = reduce(gcd, list_l)
#     return x


def combinations_count(n, r):
    r = min(r, n - r)
    numer = reduce(mul, range(n, n - r, -1), 1)
    denom = reduce(mul, range(1, r + 1), 1)
    return numer // denom


mod = 1000000007


def combinations_count_mod(n, r):
    r = min(r, n - r)
    numer = reduce(lambda x, y: x*y % mod, range(n, n - r, -1), 1)
    denom = pow(reduce(lambda x, y: x*y % mod, range(1, r + 1), 1), mod-2, mod)
    return numer * denom % mod


# def f(a_init, n):
#     # n_init=7
#     if n == 0:
#         return (a_init*10 + a_init)%K
#     else:
#         return (f(a_init, n-1)*10 + a_init)%K

a_init=7
def solve(K):
    if K%2==0 or K%5==0:
        return -1
    elif a_init%K==0:
        return 1
    else:
        dp=[a_init%K]+[0 for _ in range(K)]
        for i in range(1,K+100):
            dp[i]=(dp[i-1]*10+a_init)%K
            if dp[i]%K==0:
                return (i+1)
        return -1

def main():    
    K = int(input().strip())    
    print(solve(K))
    # print(f(7,K)%K)

if __name__ == '__main__':
    main()