99 100 100 100 100
 57 83 11 4 93
 99 99 99 99 99
 100 0 0 0 0
 0 1 2 3 4
 93 100 99 90 98
 87 38 19 33 100
 1 1 1 1 1
 0 0 0 0 1
 2 3 4 5 6
 1 2 1 2 3
 0 0 0 0 0
 100 100 100 100 100
 43 83 1 0 23
 43 83 1 100 23
 56 0 0 0 4
 99 98 98 99 100

-1
 -1
 99
 20
 2
 96
 -1
 1
 -1
 4
 -1
 -1
 100
 30
 50
 12
 -1

def arr_inp():
    return [int(x) for x in input().split()]


c = arr_inp()

while (True):
    ma, mi = max(c), min(c)
    ix_ma, ix_mi = c.index(ma), c.index(mi)
    if (ma - mi == 1 or ma == mi == 0):
        exit(print(-1))
    if (ma - mi == 0):
        exit(print(c[0]))
    c[ix_ma] -= 1
    c[ix_mi] += 1
