go sync.Once

package main

import "fmt"
import "sync"
import "time"


var oc sync.Once
var a int = 5;


func main() {
    
    go func(){
       oc.Do(func(){
           a++
       }) 
    }()
    
    
    go func(){
       oc.Do(func(){
           a++
       }) 
    }()
    
    time.Sleep(time.Second)
    
    fmt.Println(a)
}