#include <bits/stdc++.h>
using namespace std;
const long long INF = 0x3f3f3f3f;
const long long modn = 998244353;
map<int, int> mp;
vector<int> gr[2002000];
int val[2002000];
int vis[2002000];
int flag = 0;
int e, v;
int max1, max2;
void dfs(int pos) {
  v++;
  if (val[pos] > max1) {
    max2 = max1;
    max1 = val[pos];
  } else if (val[pos] > max2) {
    max2 = val[pos];
  }
  for (auto i : gr[pos]) {
    e++;
    if (vis[i] == 0) {
      vis[i] = 1;
      dfs(i);
    }
  }
}
int main() {
  int n;
  scanf("%d", &n);
  int counter = 0;
  for (int i = 1; i <= n; i++) {
    int a, b;
    scanf("%d%d", &a, &b);
    int ida = mp[a], idb = mp[b];
    if (ida == 0) {
      ida = ++counter;
      mp[a] = counter;
      val[counter] = a;
    }
    if (idb == 0) {
      idb = ++counter;
      mp[b] = counter;
      val[counter] = b;
    }
    gr[idb].push_back(ida);
    gr[ida].push_back(idb);
  }
  int ans = 0;
  for (int i = 1; i <= counter; i++) {
    if (vis[i] == 0) {
      e = 0;
      v = 0;
      max1 = max2 = 0;
      vis[i] = 1;
      dfs(i);
      e /= 2;
      if (v == e) {
        ans = max(ans, max1);
      } else if (v == e + 1) {
        ans = max(ans, max2);
      } else {
        flag = 1;
      }
    }
  }
  if (flag == 1) ans = -1;
  printf("%d\n", ans);
  return 0;
}
