Substitute

package main

import "fmt"

func main() {
    var a, b, c, d, counter int
    fmt.Scanln(&a)
    fmt.Scanln(&b)
    fmt.Scanln(&c)
    fmt.Scanln(&d)

    for k := a; k < 9; k++ {
        for l := 9; l >= b; l-- {
            for m := c; m < 9; m++ {
                for n := 9; n >= d; n-- {
                    if k % 2 == 0 && m % 2 == 0 && l % 2 == 1 && n % 2 == 1 {
                        if k == m && l == n {
                            fmt.Println("Cannot change the same player.")
                        } else {
                            fmt.Printf("%d%d - %d%d\n", k, l, m, n)
                            counter++
                            if counter == 6 {
                                return
                            }
                        }
                    }
                }
            }
        }
    }
}