2 3
1 2 1 3
1 2 1 3 2 3
 3 7
8 2 7 9 8 1
3 1 8 1 2 7 4 7 4 2 1 4 4 6
 1 10
3 9
3 2 3 4 5 3 5 7 8 6 2 5 7 8 2 4 1 7 5 1
 12 1
6 2 6 4 8 6 6 9 5 6 6 1 9 1 1 3 3 9 2 4 5 2 8 1
6 7
 2 3
1 2 7 8
1 3 2 4 7 9
 3 2
1 2 1 3 2 3
1 2 4 5
 3 8
8 9 8 5 9 2
8 4 8 3 2 6 4 2 4 3 3 7 3 6 1 6
 8 5
7 9 6 7 4 7 2 1 4 9 2 9 4 2 9 6
8 7 1 8 8 5 3 5 3 8
 4 4
1 2 1 3 6 7 6 8
1 4 1 5 6 1 6 9
 3 10
6 1 4 1 4 6
7 1 8 1 8 5 3 2 9 7 9 3 5 9 5 3 5 7 7 2
 3 3
1 2 1 3 2 3
1 2 1 3 2 3
 11 1
2 6 1 4 7 9 7 6 8 1 4 8 4 7 7 2 1 7 9 6 6 5
3 1
 5 6
1 7 5 6 6 9 3 6 1 9
2 7 2 5 8 5 4 8 4 2 8 2
 8 1
1 6 7 6 7 3 9 2 1 2 8 6 2 3 4 1
8 3
 9 4
2 8 8 9 8 1 9 2 5 9 3 5 3 2 5 2 9 1
8 4 8 7 6 8 4 7
 4 7
9 2 4 1 2 3 2 7
6 1 5 4 7 5 6 3 1 5 8 1 1 4
 3 3
1 2 5 6 7 8
2 3 4 5 8 9
 1 7
8 4
9 8 8 2 6 8 8 1 7 8 2 1 9 5
 2 2
1 2 2 3
2 3 3 4
 12 12
6 7 5 4 7 8 2 9 8 5 3 5 1 6 7 3 7 9 5 7 1 8 6 8
6 4 2 1 7 8 1 6 8 5 9 8 1 5 7 2 5 9 6 3 9 2 9 4
 9 1
3 4 3 2 3 7 3 5 9 4 1 9 6 4 5 2 7 6
8 3
 9 2
9 6 1 6 2 5 7 3 8 1 7 2 9 1 2 8 3 8
6 4 4 5
 3 9
9 7 9 2 7 2
9 8 1 9 3 9 6 3 8 6 4 6 1 3 5 4 5 3
 3 6
3 5 7 4 7 5
3 9 3 2 8 6 6 2 8 2 6 9
 2 1
1 2 1 3
1 2
 9 1
1 8 7 6 7 2 7 9 4 1 4 3 3 8 4 6 9 6
9 4
 2 2
1 2 2 4
1 2 1 3
 6 9
8 1 8 4 2 8 2 1 4 1 4 2
8 3 8 6 7 8 5 8 6 7 5 7 9 6 5 6 5 3
 12 2
3 1 8 2 6 9 2 6 5 4 4 3 4 1 4 2 6 3 9 7 9 4 3 2
7 1 4 1
 2 1
4 5 6 7
4 7
 4 3
1 2 4 5 6 7 8 9
1 2 8 9 3 1
 12 12
7 6 3 8 8 4 4 7 1 9 9 5 7 5 4 9 8 6 2 7 7 3 3 6
9 1 2 4 9 8 5 3 6 7 3 8 2 7 5 9 6 4 3 1 2 6 1 4
 12 5
9 2 6 7 7 8 3 4 8 4 7 1 2 1 7 3 7 2 5 6 3 8 1 5
3 7 7 5 7 4 5 8 4 6
 7 6
6 2 9 2 6 5 2 4 1 2 4 5 6 7
3 9 5 1 9 8 9 5 3 4 2 3
 6 4
2 7 3 2 8 3 1 5 7 4 3 5
2 6 9 8 8 6 6 9
 10 2
4 9 2 1 5 1 6 2 6 7 2 7 5 8 1 7 5 3 9 1
9 7 1 4
 4 4
1 2 2 3 1 3 4 5
1 3 3 2 1 2 4 6
 3 4
2 1 8 9 3 1
1 2 4 5 6 7 8 9
 1 12
6 8
8 4 8 2 5 8 9 8 8 3 8 7 8 1 1 3 1 9 4 3 7 3 5 7
 4 4
1 2 3 4 5 6 7 8
2 3 4 5 6 7 8 1
 3 10
1 5 7 1 2 1
9 5 5 6 3 5 4 7 8 3 9 6 8 4 9 8 4 6 3 4
 3 2
1 2 4 5 6 7
4 7 1 3
 5 6
4 7 7 3 4 3 9 4 3 9
7 5 7 8 1 7 7 2 6 2 1 2
 7 3
2 6 6 7 6 4 6 1 9 6 7 4 1 9
6 5 3 6 6 8
 2 7
2 7 2 5
7 1 9 7 8 9 4 9 8 1 3 9 3 8
 2 2
1 2 1 3
1 2 1 3
 2 11
6 1 3 6
1 7 1 2 1 5 1 4 5 3 3 2 9 8 4 2 7 5 4 9 2 9
 12 12
1 6 2 6 8 3 6 4 4 8 7 2 7 5 9 4 2 4 9 5 8 5 3 6
2 8 6 9 2 6 7 4 6 5 6 3 5 8 7 8 7 1 1 9 9 7 7 3
 4 12
2 8 3 1 2 1 9 4
9 5 5 3 1 6 3 7 7 1 8 5 6 5 4 6 1 9 1 4 2 5 9 8

-1 -1 3 6 -1 -1 0 0 -1 1 -1 1 0 -1 8 -1 0 8 0 -1 3 0 9 3 1 -1 0 8 -1 -1 1 -1 -1 -1 0 -1 -1 1 8 -1 0 -1 7 6 7 1 0 -1 -1
#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>

using namespace std;
using namespace __gnu_pbds;
typedef long long ll;
typedef long double ldb;
typedef pair<ll,ll> pll;
template <typename T> using ordered_set =  tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;

#define ff first
#define ss second
#define pb push_back
#define mp make_pair
#define V vector
#define endl "\n"
#define CLEAR(a) memset(a,0,sizeof(a))
#define all(x) x.begin(),x.end()
#define sz(x) ((ll)x.size())
#define rep0(i,n) for(ll i=0;i<n;i++)
#define rep1(i,n) for(ll i=1;i<=n;i++)
#define per(i,a,b) for(ll i=a;i>=b;i--)
#define ios_tie() ios_base::sync_with_stdio(false); cin.tie(NULL); cout.tie(NULL); cerr.tie(nullptr)
#define trace1(a)             cout <<#a<<":"<<a<< endl;
#define trace2(a,b)           cout <<#a<<":"<<a<<" | "<<#b<<":"<<b<< endl;
#define trace3(a,b,c)         cout <<#a<<":"<<a<<" | "<<#b<<":"<<b<<" | "<<#c<<":"<<c<<endl;
#define trace4(a,b,c,d)       cout <<#a<<":"<<a<<" | "<<#b<<":"<<b<<" | "<<#c<<":"<<c<<" | "<<#d<<":"<<d<<endl;

const ll inf = LLONG_MAX;
const ll mod = 1e9+7;
const ll maxn = 3e5+1;
const ldb PI = acos(-1);

void lol(ll s) {cerr<<"check........................................... "<<s<<endl;}
ll power(ll x,ll y) {ll res=1; x%=mod; while(y) {if(y&1) res=(res*x)%mod; y>>=1LL; x=(x*x)%mod; }return res;}
ll inv(ll x) {return power(x,mod-2);}//(1/x)%y = x^(y-2) % y;	// pow(x,y)%m = pow(x,y%(m-1))%m
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
ll gcd(ll a, ll b) {while(b) b ^= a ^= b ^= a %= b; return a;}

ll check(pll a, pll b)
{
	if(a.ff==b.ff && a.ss!=b.ss)
		return a.ff;
	if(a.ff==b.ss && a.ss!=b.ff)
		return a.ff;
	if(a.ss==b.ff && a.ff!=b.ss)
		return a.ss;
	if(a.ss==b.ss && a.ff!=b.ff)
		return a.ss;
	return 0;
}
int main()
{
    ios_tie();
    ll n,m;
    cin>>n>>m;
    pll a[n], b[m];
    rep0(i,n)
    	cin>>a[i].ff>>a[i].ss;
    rep0(i,m)
    	cin>>b[i].ff>>b[i].ss;
    ll freq[10] = {0};
    rep0(i,n)
    {
    	ll tmp[10] = {0};
    	rep0(j,m)
    		tmp[check(a[i],b[j])] = 1;
    	ll res, cnt = 0;
    	rep1(j,9)
    		if(tmp[j])
    			res = j, cnt++;
    	if(cnt==1)
    		freq[res] = 1;
    }
    ll res, cnt = 0;
	rep1(i,9)
		if(freq[i])
			res = i, cnt++;
	if(cnt==1)
		cout<<res<<endl;
	else if(cnt==0)
		cout<<"-1\n";
	else
		cout<<"0\n";
    return 0;
}