#include <bits/stdc++.h>

using namespace std;

int main(){
    int q;
    cin >> q;
    for(int a0 = 0; a0 < q; a0++){
        int len;
        int c;
        cin >> len >> c;
        if (len == 1) {
            if (c == 0) {
                cout << "1" << endl;
            } else {
                cout << "-1" << endl;
            }
            continue;
        }
        if (c > len*(len-1)/2) {
            cout << "-1" << endl;
            continue;
        }
        // safe zone
        
    }
    return 0;
}