func main() {
    let add1 = 1
    let add2 = 1 + 2
    let add3 = 1 + 2 + 3
    let sub1 = 1
    let sub2 = 1 - 2
    let sub3 = 1 - 2 - 3
    let mul2 = 1 * 2
    let mul3 = 1 * 2 * 3
}