//By SiriusRen

#include <cstdio>

#include <cstring>

#include <algorithm>

using namespace std;

const int N=;

int n,m,xx,yy,a,first[N],next[N*],v[N*],tot,deep[N],num[N],f[N],fa[N][];

long long ans;

int lca(int x,int y){

    if(deep[x]<deep[y])swap(x,y);

    for(int i=;~i;i--)if(deep[x]-(<<i)>=deep[y])x=fa[x][i];

    if(x==y)return x;

    for(int i=;~i;i--)if(fa[x][i]!=fa[y][i])x=fa[x][i],y=fa[y][i];

    return fa[x][];

}

void dfs(int x){for(int i=first[x];~i;i=next[i])if(v[i]!=fa[x][])deep[v[i]]=deep[x]+,fa[v[i]][]=x,dfs(v[i]);}

void add(int x,int y){v[tot]=y,next[tot]=first[x],first[x]=tot++;}

int dis(int x,int y){return deep[x]+deep[y]-*deep[lca(x,y)];}

int find(int x){return x==f[x]?x:f[x]=find(f[x]);}

int main(){

    memset(first,-,sizeof(first));

    scanf("%d%d%d",&n,&m,&a);

    for(int i=;i<n;i++){

        scanf("%d%d",&xx,&yy),add(xx,yy),add(yy,xx);

    }deep[]=,dfs();

    for(int j=;j<=;j++)

        for(int i=;i<=n;i++)

        fa[i][j]=fa[fa[i][j-]][j-];

    for(int i=;i<=m;i++)scanf("%d",&num[i]);

    for(int i=;i<=n;i++)f[i]=i;

    for(int i=;i<=m;i++){

        if(find(num[i])==num[i]){

            int LCA=lca(a,num[i]);

            ans+=dis(a,num[i]);

            for(int j=a;deep[j]>deep[LCA];j=find(fa[j][]))f[j]=LCA;

            for(int j=num[i];deep[j]>deep[LCA];j=find(fa[j][]))f[j]=LCA;

            if(f[LCA]==LCA)f[LCA]=fa[LCA][];

            a=num[i];

        }

    }

    printf("%lld\n",ans);

}