// No.1285 ゴミ捨て
package main

import (
	"bufio"
	"fmt"
	"os"
	"sort"
	"strconv"
)

func main() {
	sc := bufio.NewScanner(os.Stdin)

	sc.Scan()
	N, _ := strconv.Atoi(sc.Text())

	A := make([]int, N)
	for i := 0; i < N; i++ {
		sc.Scan()
		A[i], _ = strconv.Atoi(sc.Text())
	}

	sort.Slice(A, func(i, j int) bool { return A[i] < A[j] })

	for i := 1; i < N; i++ {
		if A[i]-A[i-1] == 1 {
			fmt.Println(2)
			return
		}
	}
	fmt.Println(1)
}