#include <bits/stdc++.h>
using namespace std;
#define int long long
#define ld long double
#define show(x,y) cout << y << " " << #x << endl;
#define show2(x,y,i,j) cout << y << " " << #x << " " << j << " " << #i << endl;
#define show3(x,y,i,j,p,q) cout << y << " " << #x << " " << j << " " << #i << " " << q << " " << #p << endl;
#define show4(x,y) for(auto it:y) cout << it << " "; cout << #x << endl;
typedef pair<int,int>pii;
typedef pair<int,pii>pi2;
void solve(){
int n;
cin >> n;
pii arr[n];
for(int x=0;x<n;x++){
cin >> arr[x].first >> arr[x].second;
}
if(n==1){
cout << -1 << "\n";
}
else if(n==2){
if(arr[0].first==arr[1].first){
cout << abs(arr[0].second-arr[1].second);
}
else if(arr[0].second==arr[1].second){
cout << abs(arr[0].second-arr[1].second);
}
else cout << -1;
}
}
int32_t main(){
ios::sync_with_stdio(0);
cin.tie(0);
int t=1;
//cin >> t;
//freopen("in.txt","r",stdin);
while(t--){
solve();
}
}
