function shouldBe(actual, expected) {
    if (actual !== expected)
        throw new Error('bad value: ' + actual);
}

{
    let date1 = new Date(2020, 1, 8, 0);
    shouldBe(date1.getTime(), 1581148800000);
    let date2 = new Date(2020, 2, 2, 0);
    shouldBe(date2.getTime(), 1583136000000);
    let date3 = new Date(2020, 2, 8, 3);
    shouldBe(date3.getTime(), 1583661600000);
    let date4 = new Date(2020, 3, 9, 3);
    shouldBe(date4.getTime(), 1586426400000);
}
{
    let date1 = new Date(2020, 11, 1, 0);
    shouldBe(date1.getTime(), 1606809600000);
    let date2 = new Date(2020, 10, 3, 0);
    shouldBe(date2.getTime(), 1604390400000);
    let date3 = new Date(2020, 10, 1, 0);
    shouldBe(date3.getTime(), 1604214000000);
    let date4 = new Date(2020, 9, 10, 0);
    shouldBe(date4.getTime(), 1602313200000);
    let date5 = new Date(2020, 6, 10, 0);
    shouldBe(date5.getTime(), 1594364400000);
}