1637C - Andrew and Stones - CodeForces Solution

def main():
    
                t = int(input())
    allans = []
    for _ in range(t):
        n = int(input())
        a = readIntArr()
        b = []
        for i in range(1, n - 1):
            b.append(a[i])
        b.sort(reverse = True)
        ans = 0
        for x in b:
            ans += (x + 1) // 2
        if len(b) == 1:
            if b[0] % 2 == 1:
                ans = -1
        elif b[0] % 2 == 1:
            if b[1] == 0:
                if b[0] % 2 == 1 and b[0] < 5:
                    ans = -1
                else:
                    ans += 1             elif b[1] == 1 and b[0] == 1:
                ans = -1
        allans.append(ans)
    multiLineArrayPrint(allans)
    
    return
 
import sys
input=sys.stdin.buffer.readline  
def oneLineArrayPrint(arr):
    print(' '.join([str(x) for x in arr]))
def multiLineArrayPrint(arr):
    print('\n'.join([str(x) for x in arr]))
def multiLineArrayOfArraysPrint(arr):
    print('\n'.join([' '.join([str(x) for x in y]) for y in arr]))
 
def readIntArr():
    return [int(x) for x in input().split()]
 
def makeArr(defaultValFactory,dimensionArr):     dv=defaultValFactory;da=dimensionArr
    if len(da)==1:return [dv() for _ in range(da[0])]
    else:return [makeArr(dv,da[1:]) for _ in range(da[0])]
 
def queryInteractive(a, b, c):
    print('? {} {} {}'.format(a, b, c))
    sys.stdout.flush()
    return int(input())
 
def answerInteractive(x1, x2):
    print('! {} {}'.format(x1, x2))
    sys.stdout.flush()
 
inf=float('inf')
 
from math import gcd,floor,ceil
import math
 
for _abc in range(1):
    main()