#include<iostream>
#include<cstring>
#include<algorithm>
using namespace std;
#define int long long
int n,b,w[24],a[110],dp[100010];
signed main() {
	cin>>n>>b;
    for(int i=1;i<=b;i++)cin>>w[i];
    for(int i=1;i<=n;i++)cin>>a[i];
    for(int i=n;i>0;i--)if(a[i-1]>0)a[i]=a[i]-a[i-1]+1;
    memset(dp,0x3f,sizeof(dp));
    dp[0]=0;
    int ans=0;
    for(int i=1;i<=b;i++)
    {
        for(int j=w[i];j<100001;j++)
        {
            dp[j]=min(dp[j],dp[j-w[i]]+1);
        }
    }
    for(int i=1;i<=n;i++)
    {
        if(dp[a[i]]==0x3f3f3f3f)
        {
            cout<<-1;
            return 0;
        }
        ans+=dp[a[i]];
    }
    cout<<ans;
    return 0;
}