#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define pb push_back

const int N=100050;
int a[N];
int cnt[N],n,m,k;

set<pair<ll,int>> all;
map<ll,vector<pair<ll,int>>> add;

void Add(int i){
	ll l=((ll)cnt[i]*n)/a[i]+1;
	ll r=((ll)(cnt[i]+1)*n+a[i]-1)/a[i];
	//printf("i:%i l:%lld r:%lld  cnt:%i n:%i  %lld / %i\n",i,l,r,cnt[i],n,(ll)(cnt[i]+1)*n,a[i]);
	if(l<=k)all.insert({r,i});
	else add[l].pb({r,i});
}

int main(){
	scanf("%i %i",&m,&k);
	for(int i=1;i<=m;i++){
		scanf("%i",&a[i]);
		n+=a[i];
	}
	for(int i=1;i<=k;i++){
		int x;
		scanf("%i",&x);
		cnt[x]++;
	}
	for(int i=1;i<=m;i++){
		Add(i);
	}
	int ans=0;
	while(k<n || k%n!=0){
		for(auto p:add[k+1])all.insert(p);
		if(all.empty())break;
		auto it=all.begin();
		//printf("Try i:%i r:%lld\n",it->second,it->first);
		if(it->first<k+1)break;
		if(next(it)!=all.end() && next(it)->first==k+1)break;
		k++;ans++;
		int i=it->second;
		all.erase(it);
		cnt[i]++;
		Add(i);
	}
	if(k<n || k%n!=0)printf("%i\n",ans);
	else printf("forever\n");
	return 0;
}