#pragma GCC optimize("Ofast")

#include "bits/stdc++.h"

#define rep(i, n) for (int i = 0; i < (n); ++i)
#define rep1(i, n) for (int i = 1; i < (n); ++i)
#define rep1n(i, n) for (int i = 1; i <= (n); ++i)
#define repr(i, n) for (int i = (n) - 1; i >= 0; --i)
#define pb push_back
#define eb emplace_back
#define all(a) (a).begin(), (a).end()
#define rall(a) (a).rbegin(), (a).rend()
#define each(x, a) for (auto &x : a)
#define ar array
#define vec vector
#define range(i, n) rep(i, n)

using namespace std;

using ll = long long;
using ull = unsigned long long;
using ld = long double;
using str = string;
using pi = pair<int, int>;
using pl = pair<ll, ll>;

using vi = vector<int>;
using vl = vector<ll>;
using vpi = vector<pair<int, int>>;
using vvi = vector<vi>;

int Bit(int mask, int b) { return (mask >> b) & 1; }

template<class T>
bool ckmin(T &a, const T &b) {
    if (b < a) {
        a = b;
        return true;
    }
    return false;
}

template<class T>
bool ckmax(T &a, const T &b) {
    if (b > a) {
        a = b;
        return true;
    }
    return false;
}

// [l, r)
template<typename T, typename F>
T FindFirstTrue(T l, T r, const F &predicat) {
    --l;
    while (r - l > 1) {
        T mid = l + (r - l) / 2;
        if (predicat(mid)) {
            r = mid;
        } else {
            l = mid;
        }
    }
    return r;
}


template<typename T, typename F>
T FindLastFalse(T l, T r, const F &predicat) {
    return FindFirstTrue(l, r, predicat) - 1;
}


const ll INF = 2e18;
const int INFi = 1e9;
const int N = 30 + 5;
const int LG = 20;


void solve() {
    int n; cin >> n;
    vl t(n), c(n);
    rep(i, n) cin >> t[i] >> c[i];
    for(int i = 1; i + 1 < n; ++i) {
        if (t[i - 1] == t[i] && t[i] == t[i + 1]) {
            cout << "-1\n";
            return;
        }
    }
    if (set<int>(all(c)).size() <= 2) {
        cout << "0\n";
        return;
    }
    int L = 0;
    int R = (int)1e9 + 1;
    while (R - L > 1) {
        int v = (L + R) / 2;
        vector<pair<ll, ll>> pts(n);
        rep(i, n) {
            pts[i].first = t[i] * v + c[i];
            pts[i].second = t[i] * v - c[i];
        }
        sort(all(pts));
        ll x = -INF, y = -INF;
        bool ok = true;
        for(auto &[_, val] : pts) {
            if (val >= x) {
                x = val;
                continue;
            }
            if (val >= y) {
                y = val;
                continue;
            }
            ok = false;
            break;
        }
        if (ok) {
            R = v;
        } else {
            L = v;
        }
    }
    cout << R << '\n';
}


signed main() {
    ios_base::sync_with_stdio(false);
    cin.tie(0);
    cout << setprecision(12) << fixed;
    int t = 1;
    cin >> t;
    rep(i, t) {
        solve();
    }
    return 0;
}