//STATUS:C++_AC_828MS_11284KB
#include <functional>
#include <algorithm>
#include <iostream>
//#include <ext/rope>
#include <fstream>
#include <sstream>
#include <iomanip>
#include <numeric>
#include <cstring>
#include <cassert>
#include <cstdio>
#include <string>
#include <vector>
#include <bitset>
#include <queue>
#include <stack>
#include <cmath>
#include <ctime>
#include <list>
#include <set>
//#include <map>
using namespace std;
//#pragma comment(linker,"/STACK:102400000,102400000")
//using namespace __gnu_cxx;
//define
#define pii pair<int,int>
#define mem(a,b) memset(a,b,sizeof(a))
#define lson l,mid,rt<<1
#define rson mid+1,r,rt<<1|1
#define PI acos(-1.0)
//typedef
typedef long long LL;
typedef unsigned long long ULL;
//const
const int N=1010;
const int INF=0x3f3f3f3f;
const int MOD=1e9+7,STA=8000010;
//const LL LNF=1LL<<60;
const double EPS=1e-8;
const double OO=1e15;
const int dx[4]={-1,0,1,0};
const int dy[4]={0,1,0,-1};
const int day[13]={0,31,28,31,30,31,30,31,31,30,31,30,31};
//Daily Use ...
inline int sign(double x){return (x>EPS)-(x<-EPS);}
template<class T> T gcd(T a,T b){return b?gcd(b,a%b):a;}
template<class T> T lcm(T a,T b){return a/gcd(a,b)*b;}
template<class T> inline T lcm(T a,T b,T d){return a/d*b;}
template<class T> inline T Min(T a,T b){return a<b?a:b;}
template<class T> inline T Max(T a,T b){return a>b?a:b;}
template<class T> inline T Min(T a,T b,T c){return min(min(a, b),c);}
template<class T> inline T Max(T a,T b,T c){return max(max(a, b),c);}
template<class T> inline T Min(T a,T b,T c,T d){return min(min(a, b),min(c,d));}
template<class T> inline T Max(T a,T b,T c,T d){return max(max(a, b),max(c,d));}
//End

struct Edge{
    int u,v;
}e[N*10*2];
int first[N],next[N*10*2],vis[N],hig[N];
int n,m,L,mt;

void adde(int a,int b)
{
    e[mt].u=a,e[mt].v=b;
    next[mt]=first[a],first[a]=mt++;
    e[mt].u=b,e[mt].v=a;
    next[mt]=first[b],first[b]=mt++;
}

queue<int> q;
void bfs()
{
    int i,j,u,v;
    while(!q.empty())
    {
        u=q.front();q.pop();
        for(i=first[u];i!=-1;i=next[i]){
            v=e[i].v;
            if(vis[v])continue;
            vis[v]=1;
            hig[v]=hig[u]+1;
            q.push(v);
        }
    }
}

int main()
{
 //   freopen("in.txt","r",stdin);
    int i,j,k,a,b,c;
    while(~scanf("%d%d%d",&n,&m,&L))
    {
        mem(first,-1);mt=0;
        mem(hig,INF);
        mem(vis,0);
        for(i=0;i<m;i++){
            scanf("%d",&a);
            hig[a]=0;
            q.push(a);
            vis[a]=1;
        }
        for(i=0;i<L;i++){
            scanf("%d%d",&a,&b);
            adde(b,a);
        }

        bfs();
        int ans=0,answ=0;
        for(i=0;i<n;i++){
            if(hig[i]>ans){
                ans=hig[i];
                answ=i;
            }
        }

        printf("%d\n",answ);
    }
    return 0;
}