#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <algorithm>
#include <assert.h>
#define IOS ios::sync_with_stdio(false)
using namespace std;
#define inf (0x3f3f3f3f)
typedef long long int LL;


#include <iostream>
#include <sstream>
#include <vector>
#include <set>
#include <map>
#include <queue>
#include <string>
#include <bitset>
int calc_min(int val) {
    if (val == 1) return 0;
    if (val == 2) return 1;
    return 2 * (val - 2);
}
void work() {
    int len, c;
    cin >> len >> c;
    if (1LL * len * (len - 1) / 2 < c || c < calc_min(len)) {
        cout << "-1" << endl;
        return;
    }
    
}

int main() {
#ifdef local
    freopen("data.txt", "r", stdin);
//    freopen("data.txt", "w", stdout);
#endif
    IOS;
    int t;
    cin >> t;
    while (t--)
        work();
    return 0;
}