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#include <bits/stdc++.h>
using namespace std;
typedef long long int ll;
#define endl "\n"
#define int long long
 
const double PI = 3.14159265358979;
const ll INF =  1e18;
const ll MOD = 1e9 + 7;
const ll nax = 100002;
const int LOG = 25;
 

class Solver {

    int n;
    vector<vector<int> > adj;
    vector<int> depth;
    vector<int> parent;

    void dfs(int u, int par, int dep) {
        parent[u] = par;
        depth[u] = dep;

        for (int v: adj[u]) {
            if (v != par) {
                dfs(v, u, dep + 1);
            }
        }
    }

public:
 
    void solve() {
        cin >> n;
        adj.resize(n + 1);
        parent.resize(n + 1);
        depth.resize(n + 1);

        for (int i = 1; i < n; i++) {
            int x, y;
            cin >> x >> y;
            adj[x].push_back(y);
            adj[y].push_back(x);
        }

        dfs(1, 0, 0);
        int d1 = 0, n1 = 1;
        for (int i = 1; i <= n; i++) {
            if (d1 < depth[i]) {
                d1 = depth[i];
                n1 = i;
            }
        }

        dfs(n1, 0, 0);
        d1 = 0, n1 = 1;
        for (int i = 1; i <= n; i++) {
            if (d1 < depth[i]) {
                d1 = depth[i];
                n1 = i;
            }
        }

        if (d1 & 1) {
            cout << "-1" << endl;
            return;
        }

        int x = d1 / 2;
        while(x--) {
            n1 = parent[n1];            
        }

        cout << n1 << endl;
    }
};


signed main() {
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    cout.tie(nullptr);
 
    int t = 1;
    // cin >> t;
    while(t--) {
        Solver solver;
        solver.solve();
    }
 
    return 0;
}