# -*- coding: utf-8 -*-
"""
No.395 永遠の17歳
https://yukicoder.me/problems/no/395

"""
import sys
from sys import stdin
input = stdin.readline


def main(args):
    A = int(input())
    ans = A - 7
    if ans <= 0:
        print(-1)
    else:
        print(ans)


if __name__ == '__main__':
    main(sys.argv[1:])