```go
package main

import (
	"bufio"
	"fmt"
	"os"
)

func main() {
	in := bufio.NewReader(os.Stdin)
	out := bufio.NewWriter(os.Stdout)
	defer out.Flush()

	var t int
	if _, err := fmt.Fscan(in, &t); err != nil {
		return
	}
	for ; t > 0; t-- {
		var n, k int64
		fmt.Fscan(in, &n, &k)
		a := n / k
		r := n % k
		h := k / 2
		if r > h {
			r = h
		}
		fmt.Fprintln(out, k*a+r)
	}
}
```