#include <bits/stdc++.h>

using namespace std;
                        
const int N = 100010;

int n, l[N], r[N], kol[N], mn[N], mx[N], ans;
bool ok;

void dfs(int p)
{
	if (l[p] == -1)
	{
		kol[p] = 1;
		mn[p] = r[p];
		mx[p] = r[p];
		return;
	} 	
	dfs(l[p]);
	dfs(r[p]);
	mn[p] = min(mn[l[p]], mn[r[p]]);
	mx[p] = max(mx[l[p]], mx[r[p]]);
	kol[p] = kol[l[p]] + kol[r[p]];
	if (kol[p] != mx[p] - mn[p] + 1) ok = false;
	if (mn[l[p]] > mn[r[p]]) ans++;
}

void solve()
{
	cin >> n;
	for (int i = 0; i < n; i++)
	{
		cin >> l[i] >> r[i];
		r[i]--;
		if (l[i] != -1)	l[i]--;
	}
	ok = true;
	ans = 0;
	dfs(0);
	if (!ok)
		cout << "-1\n";
	else
		cout << ans << "\n";
}
        
int main() 
{
	cin.sync_with_stdio(0);
	int T;
	cin >> T;
	for (int i = 0; i < T; i++)
		solve();
	return 0;
}