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a = int(input())
b = int(input())
c = int(input())
d = int(input())

v1 = max(a + c, b, d)
v2 = max(a + d, b, c)
v3 = max(b + c, a, d)
v4 = max(b + d, a, c)

ans = min(v1, v2, v3, v4, max(a, c, b + d), max(a, d, b + c))

print(ans)