#include<bits/stdc++.h>
#define rep(i,a,n) for (int i = a;i < n;i++)
#define per(i,n,a) for (int i = n-1;i >= a;i--)
using namespace std;

int main() {
    int n; cin >> n;
    int x[n],y[n];
    rep(i,0,n){
        cin >> x[i] >> y[i];
        if(x[i] + n != y[i]){
            cout << "-1" << endl;
            break;
        }else{
            cout << n << endl;
        }
    }
}