#include <iostream>
#include <algorithm>

using namespace std;

int main() {
    int T;
    cin >> T;
    while (T--) {
        int N, K;
        cin >> N >> K;
        int X = max(0, K - N);
        int Y = 0;
        if (N > 0) {
            Y = 1;
        }
        cout << X * Y << endl;
    }
    return 0;
}