#include <bits/stdc++.h>   using namespace std;   const int M = 15, N = 15;   int m, n;   pair<int, int> a[M], b[N];   vector<int> tot, cur;   int main() {     ios_base::sync_with_stdio(false);     cin.tie(nullptr);     cin >> m >> n;     for (int i = 1; i <= m; i++) {       cin >> a[i].first >> a[i].second;     }     for (int i = 1; i <= n; i++) {       cin >> b[i].first >> b[i].second;     }     for (int i = 1; i <= m; i++) {       cur.clear();       for (int j = 1; j <= n; j++) {         int cnt = 0;         if (a[i].first == b[j].first || a[i].first == b[j].second) {           cnt++;         }         if (a[i].second == b[j].first || a[i].second == b[j].second) {           cnt++;         }         if (cnt == 1) {           if (a[i].first == b[j].first || a[i].first == b[j].second) {             cur.push_back(a[i].first);           } else {             cur.push_back(a[i].second);           }         }       }       sort(cur.begin(), cur.end());       cur.erase(unique(cur.begin(), cur.end()), cur.end());       if (cur.size() >= 2) {         return cout << -1, 0;       } else if (cur.size() == 1) {         tot.push_back(cur[0]);       }     }     for (int i = 1; i <= n; i++) {       cur.clear();       for (int j = 1; j <= m; j++) {         int cnt = 0;         if (b[i].first == a[j].first || b[i].first == a[j].second) {           cnt++;         }         if (b[i].second == a[j].first || b[i].second == a[j].second) {           cnt++;         }         if (cnt == 1) {           if (b[i].first == a[j].first || b[i].first == a[j].second) {             cur.push_back(b[i].first);           } else {             cur.push_back(b[i].second);           }         }       }       sort(cur.begin(), cur.end());       cur.erase(unique(cur.begin(), cur.end()), cur.end());       if (cur.size() >= 2) {         return cout << -1, 0;       } else if (cur.size() == 1) {         tot.push_back(cur[0]);       }     }     sort(tot.begin(), tot.end());     tot.erase(unique(tot.begin(), tot.end()), tot.end());     if (tot.size() >= 2) {       cout << 0;     } else {       cout << tot[0];     }   }   