#include<bits/stdc++.h> using namespace std; int main(){ //freopen("tree.in","r",stdin); //freopen("tree.out","w",stdout); int n; cin>>n; for(int i=1;i<n;i++){ int x,y; cin>>x>>y; } if(n%2==0) cout<<-1<<endl; else cout<<(n/2)+2<<endl; }