main.go

package main

import (
	"fmt"
	"time"
)

func now() int64 {
	return time.Now().UnixNano() / int64(time.Millisecond)
}

func measure(task func()) int64 {
	start := now()
	task()
	return now() - start
}

func printPI() {
	var result float64
	isOdd := false

	for i := float64(1); i < 10000000000; i += 2 {
		delta := 1 / i

		if isOdd {
			result -= delta
		} else {
			result += delta
		}

		isOdd = !isOdd
	}

	fmt.Println(result * 4)
}

func main() {
	fmt.Println(measure(printPI))
}