Go Data Type uint64 Calculate Factorial

package main//from w w w  .j  a va2 s . c o m
import "fmt"

var factVal uint64 = 1 
var i int = 1
var n int

func factorial(n int) uint64 {   
    if(n < 0){
        fmt.Print("Factorial of negative number doesn't exist.")    
    }else{        
        for i:=1; i<=n; i++ {
            factVal *= uint64(i)  // mismatched types int64 and int
        }
        
    }    
    return factVal
}

func main(){    
    n = 10   
    fmt.Print("Factorial is: ",factorial(n))
}