题解 | #分苹果#

import sys


def avg_cut(l):
    b = False
    for k in l:
        if abs(sum(l)/len(l) -k)%2 ==0:
            b = True
        else:
            b = False
            break
    return b

m = 0 
n = int(input())
l= input().split()
l2 = [int(x) for x in l]
bb= avg_cut(l2)
if len(l2) ==1:
    print(0)       
elif sum(l2) % len(l2) == 0 and bb :                 
    while len(set(l2)) != 1:              
        l2[l2.index(max(l2))] = max(l2) - 2  
        l2[l2.index(min(l2))] = min(l2) + 2  
        m += 1
    print(m)                              
else:                                    
    print(-1)