package main

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

type FastScanner struct {
	r *bufio.Reader
}

func NewFastScanner() *FastScanner {
	return &FastScanner{r: bufio.NewReaderSize(os.Stdin, 1<<20)}
}

func (fs *FastScanner) NextInt() int {
	sign, val := 1, 0
	c, err := fs.r.ReadByte()
	for (c < '0' || c > '9') && c != '-' {
		c, err = fs.r.ReadByte()
		if err != nil {
			return 0
		}
	}
	if c == '-' {
		sign = -1
		c, _ = fs.r.ReadByte()
	}
	for c >= '0' && c <= '9' {
		val = val*10 + int(c-'0')
		c, err = fs.r.ReadByte()
		if err != nil {
			break
		}
	}
	if err == nil {
		_ = fs.r.UnreadByte()
	}
	return sign * val
}

func min(a, b int) int {
	if a < b {
		return a
	}
	return b
}

func main() {
	in := NewFastScanner()
	n := in.NextInt()
	prev := in.NextInt()
	runs := make([]int, 0, n)
	cnt := 1
	for i := 1; i < n; i++ {
		x := in.NextInt()
		if x == prev {
			cnt++
		} else {
			runs = append(runs, cnt)
			prev = x
			cnt = 1
		}
	}
	runs = append(runs, cnt)

	ans := 0
	for i := 0; i+1 < len(runs); i++ {
		v := 2 * min(runs[i], runs[i+1])
		if v > ans {
			ans = v
		}
	}
	fmt.Println(ans)
}