#include <bits/stdc++.h>
using namespace std;
inline int read()
{
int x=0,f=1,c=getchar();
while(c<48) c=='-'&&(f=-1),c=getchar();
while(c>47) x=x*10+c-'0',c=getchar();
return x*f;
}
typedef long long ll;
const ll MAXN = 2000005;
struct Edge {ll to,val;};
std::vector<Edge> G[MAXN];
ll s[MAXN<<2],dis[MAXN],st[MAXN],size[MAXN];
ll dfnl[MAXN],ispt[MAXN],dfnr[MAXN];
ll n,m,top,dft=1;
ll sumdis,ans=2e18;
inline void addedge(ll u,ll v,ll w)
{
G[u].push_back(Edge{v,w});
G[v].push_back(Edge{u,w});
}
inline int gcd(int a,int b)
{return b ? gcd(b,a%b) : abs(a);}
void pushup(int rt)
{
s[rt]=gcd(s[rt<<1],s[rt<<1|1]);
}
void build(int l=1,int r=m,int rt=1)
{
if(l==r) return void(s[rt]=dis[st[l]]-dis[st[l-1]]);
int mid=(l+r)>>1;
build(l,mid,rt<<1); build(mid+1,r,rt<<1|1);
pushup(rt);
}
void update(int p,int k,int l=1,int r=m,int x=1)
{
if(l==r) return s[x]+=k,void();
int mid=(l+r)>>1;
if(p<=mid) update(p,k,l,mid,x<<1);
if(p>mid) update(p,k,mid+1,r,x<<1|1);
pushup(x);
}
ll query() {return abs(s[1]);}
ll sum,ans=1e18;
void dfs(int u,int fa=0)
{
if(ispt[u])
{
st[dfnl[u]=++dfnl[0]]=u;
sum+=dis[u]; size[u]=1;
}
else
{
dfnl[u]=dfnl[0]+1;
}
for(Edge e : G[u])
{
if(e.to==fa) continue;
dis[e.to]=dis[u]+e.val;
dfs(e.to,u); size[u]+=size[e.to];
}
dfnr[u]=dfnl[0];
}
void modify(int l,int r,int x)
{
if(l>r)return;
update(l,x); if(r<m)update(r+1,-x);
}
void solve(int u,int fa=0)
{
if(query()) ans=min(ans,sum/query());
for(Edge e : G[u])
{
if(e.to==fa) continue;
sum+=1ll*(m-size[e.to]*2)*e.val;
modify(1,dfnl[e.to]-1,e.val);
modify(dfnl[e.to],dfnr[e.to],-e.val);
modify(dfnr[e.to]+1,m,e.val);
solve(e.to,u);
sum-=1ll*(m-size[e.to]*2)*e.val;
modify(1,dfnl[e.to]-1,-e.val);
modify(dfnl[e.to],dfnr[e.to],e.val);
modify(dfnr[e.to]+1,m,-e.val);
}
}
int main()
{
n=read(); m=read();
if(m==1) return puts("0"),0;
for(int i=1,x; i<=m; i++) ispt[read()]=1;
for(int i=1; i<n; ++i)
{
int u=read(),v=read(),w=read();
addedge(u,v,w);
}
dfs(1); build(); solve(1);
printf("%lld\n", ans*2);
return 0;
}