#include <bits/stdc++.h>
using namespace std;
#define int long long
const int modulo = 1e9+7;
int32_t main(){
ios_base::sync_with_stdio(false);
cin.tie(nullptr);
int n;
cin >> n;
vector<vector<int>> adj(n+1);
for(int i=1;i<=n;i++){
int a,b;
cin >> a >> b;
adj[a].emplace_back(b);
adj[b].emplace_back(a);
}
vector<bool> visited(n+1);
vector<int> myLevel(n+1);
vector<int> ans(4);
int anss = -1;
function<void(int,int,int)> dfs = [&](int x,int p,int level){
visited[x]=true;
ans[level]++;
myLevel[x]=level;
for(int&i:adj[x])if(i!=p){
if(visited[i]){
if(((myLevel[x]+1)&3) == myLevel[i])anss=(myLevel[x]+2)&3;
if(((myLevel[i]+1)&3) == myLevel[x])anss=(myLevel[i]+2)&3;
continue;
}
dfs(i,x,(level+1)&3);
}
};
dfs(1,0,0);
if(anss==-1){
cout << "-1\n";
} else cout << ans[anss]+ans[(anss+1)&3] << '\n';
}
