package main

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

type FastScanner struct {
	r *bufio.Reader
}

func NewFastScanner() *FastScanner {
	return &FastScanner{r: bufio.NewReader(os.Stdin)}
}

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

func gcd(a, b int) int {
	for b != 0 {
		a, b = b, a%b
	}
	if a < 0 {
		return -a
	}
	return a
}

func powmod(a, e, mod int64) int64 {
	res := int64(1)
	base := a % mod
	for e > 0 {
		if e&1 == 1 {
			res = (res * base) % mod
		}
		base = (base * base) % mod
		e >>= 1
	}
	return res
}

func combSmallK(n, k int, mod int64, invFactK int64) int64 {
	if n < k {
		return 0
	}
	if k == 0 {
		return 1
	}
	res := int64(1)
	for i := 0; i < k; i++ {
		res = (res * int64(n-i)) % mod
	}
	res = (res * invFactK) % mod
	return res
}

func main() {
	in := NewFastScanner()
	n := in.NextInt()
	arr := make([]int, n)
	maxV := 0
	g := 0
	hasOne := false
	for i := 0; i < n; i++ {
		x := in.NextInt()
		arr[i] = x
		if x == 1 {
			hasOne = true
		}
		if x > maxV {
			maxV = x
		}
		g = gcd(g, x)
	}
	if hasOne {
		fmt.Println(1)
		return
	}
	if g > 1 {
		fmt.Println(-1)
		return
	}

	freq := make([]int, maxV+1)
	for _, v := range arr {
		freq[v]++
	}

	cnt := make([]int, maxV+1)
	for d := 1; d <= maxV; d++ {
		s := 0
		for m := d; m <= maxV; m += d {
			s += freq[m]
		}
		cnt[d] = s
	}

	mu := make([]int8, maxV+1)
	isComp := make([]bool, maxV+1)
	primes := make([]int, 0, 30000)
	mu[1] = 1
	for i := 2; i <= maxV; i++ {
		if !isComp[i] {
			primes = append(primes, i)
			mu[i] = -1
		}
		for _, p := range primes {
			ip := i * p
			if ip > maxV {
				break
			}
			isComp[ip] = true
			if i%p == 0 {
				mu[ip] = 0
				break
			} else {
				mu[ip] = -mu[i]
			}
		}
	}

	nonZeroMu := make([]int, 0)
	for d := 1; d <= maxV; d++ {
		if mu[d] != 0 && cnt[d] > 0 {
			nonZeroMu = append(nonZeroMu, d)
		}
	}

	const MOD1 int64 = 1000000007
	const MOD2 int64 = 1000000009
	const MOD3 int64 = 998244353

	factK := [8]int64{1, 1, 2, 6, 24, 120, 720, 5040}
	invFact1 := [8]int64{}
	invFact2 := [8]int64{}
	invFact3 := [8]int64{}
	for k := 0; k <= 7; k++ {
		invFact1[k] = powmod(factK[k], MOD1-2, MOD1)
		invFact2[k] = powmod(factK[k], MOD2-2, MOD2)
		invFact3[k] = powmod(factK[k], MOD3-2, MOD3)
	}

	for k := 2; k <= 7; k++ {
		var s1, s2, s3 int64
		for _, d := range nonZeroMu {
			c := cnt[d]
			if c < k {
				continue
			}
			v1 := combSmallK(c, k, MOD1, invFact1[k])
			v2 := combSmallK(c, k, MOD2, invFact2[k])
			v3 := combSmallK(c, k, MOD3, invFact3[k])
			if mu[d] > 0 {
				s1 += v1
				if s1 >= MOD1 {
					s1 -= MOD1
				}
				s2 += v2
				if s2 >= MOD2 {
					s2 -= MOD2
				}
				s3 += v3
				if s3 >= MOD3 {
					s3 -= MOD3
				}
			} else { // mu[d] < 0
				s1 -= v1
				if s1 < 0 {
					s1 += MOD1
				}
				s2 -= v2
				if s2 < 0 {
					s2 += MOD2
				}
				s3 -= v3
				if s3 < 0 {
					s3 += MOD3
				}
			}
		}
		if s1 != 0 || s2 != 0 || s3 != 0 {
			fmt.Println(k)
			return
		}
	}
	// Should not reach here due to bounds; fallback
	fmt.Println(7)
}