mod = 1000000007
eps = 10**-9


def main():
    import sys
    input = sys.stdin.readline

    a, b, n, m = map(int, input().split())
    ok = min(a, b)
    ng = max(a, b) + 1
    mid = (ok + ng) // 2
    while ng - ok > 1:
        if a > b:
            if b + (a - mid) // n >= mid:
                ok = mid
            else:
                ng = mid
        else:
            if a + (b - mid) // m >= mid:
                ok = mid
            else:
                ng = mid
        mid = (ok+ng) // 2
    print(ok)


if __name__ == '__main__':
    main()