put("Enter an operation (+, -, *, /): ")
op := getln()
if (!(op == "+" || op == "-" || op == "*" || op == "/")) {
	put("Unknown operation: ")
	putln(op)
} else {
	put("1st number: ")
	n1 := float(getln())
	put("2nd number: ")
	n2 := float(getln())

	put("Result: ")
	if (op == "+")
		putln(n1 + n2)
	else if (op == "-")
		putln(n1 - n2)
	else if (op == "*")
		putln(n1 * n2)
	else if (op == "/")
		putln(n1 / n2)
}