//Author: Kevin
#include<bits/stdc++.h>
//#pragma GCC optimize("O2")
using namespace std;
#define pb emplace_back
#define mp make_pair
#define ALL(x) (x).begin(),(x).end()
#define rALL(x) (x).rbegin(),(x).rend()
#define srt(x) sort(ALL(x))
#define rev(x) reverse(ALL(x))
#define rsrt(x) sort(rALL(x))
#define sz(x) (int)(x.size())
#define inf 0x3f3f3f3f
#define lb(v,x) (int)(lower_bound(ALL(v),x)-v.begin())
#define ub(v,x) (int)(upper_bound(ALL(v),x)-v.begin())
#define uni(v) v.resize(unique(ALL(v))-v.begin())
using ll=long long;
using ull=unsigned long long;
using pii=pair<int,int>;
using i128=__int128;
void die(string S){puts(S.c_str());exit(0);}
int n,k;
int a[100100],b[200200];
int c[100100];
int psum[300300];
int pos[300300];
int main()
{
	ios::sync_with_stdio(false);
	cin.tie(0);
	cout.tie(0);
	cin>>n>>k;
	for(int i=1;i<=n;i++)
		cin>>a[i];
	for(int i=1;i<=n;i++)
		pos[a[i]]=i;
	memcpy(c,a,sizeof(c));
	sort(c+1,c+n+1);
	for(int i=1;i<=k;i++)
	{
		cin>>b[i];
		psum[b[i]]++;
	}
	for(int i=1;i<=n+k;i++)
		psum[i]+=psum[i-1];
	int ans=n+n;
	for(int l=1;l<=n;l++)
	{
		int r=l;
		while(r<=n&&pos[c[r+1]]>pos[c[r]]) r++;
		int L1=l-1,R1=n-r;
		int L2=psum[c[l-1]],R2=k-psum[c[r+1]];
		if(r==n) R2=0;
		int M2=k-L2-R2;
		int rr=max(L1*2,R1*2-1);
		R1-=(M2+1)/2;
		L1-=M2/2;
		L1=max(L1,0);
		R1=max(R1,0);
		if(M2&1)
		{
			swap(L1,R1);
			swap(L2,R2);
		}
		if(!L1&&!R1) ans=min(ans,rr);
		if(R1&&!L1&&L2>=R1*2-1) ans=min(ans,M2+R1*2-1);
		if(L1&&!R1&&R2>=L1*2) ans=min(ans,M2+L1*2);
		if(R1&&L1+R1>1&&L2>=(R1-1)*2&&R2>=(R1-1+L1)*2-1&&L2+R2>=(R1-1)*2+(R1-1+L1)*2) ans=min(ans,M2+(R1-1)*2+(R1-1+L1)*2);
		if(L2&&R2>=L1*2-1&&L2>=(R1+L1)*2&&L2+R2>=(R1+L1+L1)*2) ans=min(ans,M2+(R1+L1+L1)*2);
		int L=max(L1*2,R1*2-1),R=k-M2;
		while(L<R)
		{
			int mid=(L+R)/2;
			int can=min(mid/2,L2)+min((mid+1)/2,R2);
			if(can>=mid)
				R=mid;
			else
				L=mid+1;
		}
		// ans=min(ans,L+M2);
		l=r;
	}
	if(ans>k) die("-1");
	cout<<ans<<'\n';
	return 0;
}