#include<stdio.h>
#include<algorithm>
#include<math.h>
#include<string.h>
#include<queue>
#include<stack>
#include<vector>
#include<map>
#include<set>
using namespace std;

typedef long long ll;
typedef pair<int,int> pii;
const int N=5e5+86;

int n,k;
ll ans=0x7f7f7f7f7f7f7f7f;
struct edge{int to,nxt,w;}e[N];
int head[N],tot;
void add(int u,int v,int w){e[++tot]={v,head[u],w},head[u]=tot;}

ll a[N],sum;
struct Segment_Tree
{
    int l,r;
    ll g;
}t[N<<2];
void push_up(int o){t[o].g=__gcd(t[o<<1].g,t[o<<1|1].g);}
void build(int o,int l,int r)
{
    t[o].l=l,t[o].r=r;
    if(l==r){t[o].g=a[l]-a[l-1];return;}
    int mid=l+r>>1;
    build(o<<1,l,mid);
    build(o<<1|1,mid+1,r);
    push_up(o);
}
void update(int o,int x,ll k)
{
    if(t[o].l==t[o].r){t[o].g+=k;return;}
    if(x<=t[o<<1].r) update(o<<1,x,k);
    else update(o<<1|1,x,k);
    push_up(o);
}
struct node
{
    int in,out;
    bool f;
}p[N];
int cnt;
int dfs1(int u,int fa,ll dep)
{
    p[u].in=cnt+1;
    if(p[u].f) a[++cnt]=dep,p[u].out=cnt,sum+=dep;
    // printf("%d %lld\n",u,dep);
    for(int i=head[u];i;i=e[i].nxt)
    {
        int v=e[i].to,w=e[i].w;
        if(v==fa) continue;
        p[u].out=max(p[u].out,dfs1(v,u,dep+w));
    }
    // printf("%d %d %d\n",u,p[u].in,p[u].out);
    return p[u].out;
}
void dfs2(int u,int fa)
{
    ans=min(ans,sum*2/abs(t[1].g));//printf("%lld %lld\n",sum,abs(t[1].g));
    for(int i=head[u];i;i=e[i].nxt)
    {
        int v=e[i].to;
        ll w=e[i].w;
        if(v==fa) continue;
        sum+=-(p[v].in<=p[v].out)*(p[v].out-p[v].in+1)*w+(k-(p[v].in<=p[v].out)*(p[v].out-p[v].in+1))*w;
        if(p[v].in<=p[v].out)
        {
            update(1,1,w);
            update(1,p[v].in,-2*w);
            if(p[v].out<k) update(1,p[v].out+1,2*w);
        }
        dfs2(v,u);
        sum+=(p[v].in<=p[v].out)*(p[v].out-p[v].in+1)*w-(k-(p[v].in<=p[v].out)*(p[v].out-p[v].in+1))*w;
        if(p[v].in<=p[v].out)
        {
            update(1,1,-w);
            update(1,p[v].in,2*w);
            if(p[v].out<k) update(1,p[v].out+1,-2*w);
        }
    }
}

template<typename T>
inline void read(T &x)
{
    T k=1;char ch=getchar();x=0;
    while(ch<'0'||ch>'9'){if(ch=='-') k=-1;ch=getchar();}
    while(ch>='0'&&ch<='9')x=(x<<1)+(x<<3)+(ch^48),ch=getchar();
    x*=k;
}

signed main()
{
    read(n),read(k);
    for(int i=1,x;i<=k;i++)
    {
        read(x);
        p[x].f=true;
    }
    for(int i=1,u,v,w;i<=n-1;i++)
        read(u),read(v),read(w),add(u,v,w),add(v,u,w);
    dfs1(1,0,0);
    build(1,1,k);
    dfs2(1,0);
    printf("%lld\n",ans);
    return 0;
}