# -*- coding: utf-8 -*-
"""
Created on Sat Jul  6

@author: Jiang.Lijin
"""

def calc7(args):
    #空白なら‐1を返す
    if len(args) == 0:
        return -1
    ret = 0
    b = 0
    for n in args:
        #直前の数字が7の場合はフラグ１、数字を2倍
        if b == 1:
            ret = ret + int(n)*2
            b = 0
            continue

        ret += n

        #数字が7の場合はフラグをON
        if n == 7:
            b = 1
    return ret


print(calc7([1, 2]))
print(calc7([3, 7]))
print(calc7([7, 5, 6]))
print(calc7([7, 9, 7, 9, 7, 9]))
print(calc7([]))