#include <bits/stdc++.h>
#define ent '\n'
#define f first
#define s second
#define int long long

using namespace std;
typedef long long ll;
const int maxn = 1e6 + 12;
const int mod = 1e9 + 7;

int x[maxn], y[maxn];
int p[maxn];
int n, m, s;

int get(int x){
    if(p[x] == x) return x;
    return p[x] = get(p[x]);
}

int pos(int x, int y){
    return x * 400 + y;
}

void solve(){
    cin >> n;
    if(n <= 2){
        cout << "-1\n";
        return;
    }
    int mnx = 1e9, mny = 1e9;
    for(int i=1;i<=n;i++){
        cin >> x[i] >> y[i];
        x[i] += 305, y[i] += 305;
        mnx = min(mnx, x[i]);
        mny = min(mny, y[i]);
    }
    for(int i=0;i<1000;i++){
        for(int j=0;j<1000;j++){
            p[i*400 + j] = i * 400 + j;
        }
    }
    for(int i=1;i<=n;i++){
        for(int j=i+1;j<=n;j++){
            for(int dx=-205;dx<=205;dx++){
                for(int dy=-205;dy<=205;dy++){
                    p[get(pos(x[i] + dx, y[i] + dy))] = get(pos(x[j] + dx, y[j] + dy));
                }
            }
        }
    }
    set<int> s, t;
    for(int i=mnx;i<=mnx+100;i++){
        for(int j=mny;j<=mny+100;j++){
            s.insert(get(pos(i, j)));
        }
    }
    for(int i=mnx-100;i<=mnx+100;i++){
        for(int j=mny-100;j<=mny+100;j++){
            t.insert(get(pos(i, j)));
        }
    }
    if(s.size() != t.size()){
        cout << "-1\n";
    }
    else{
        cout << s.size() << ent;
    }
}

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