import io
import sys

sys.stdin = io.StringIO('''2 60 3 96''')  # 12 / 6

a = list(map(int, input().split()))
_min, _max = min(a), max(a)
k = 0
for i in range(_min, _max):
    if i % a[0] + i % a[2] + a[1] % i + a[3] % i == 0:
        k += 1
        print(i)
        break

if k == 0:
    print(-1)