#include "bits/stdc++.h"
using namespace std;

typedef long long ll;
typedef pair<int, int> pii;
typedef vector<int> vi;

#define all(v) v.begin(), v.end()
#define pb push_back    
#define sz(x) (int)(x).size()

#define deb(...) logger(#__VA_ARGS__, __VA_ARGS__)
template<typename ...Args>
void logger(string vars, Args&&... values) {
  cout << vars << " = ";
  string delim = "";
  (..., (cout << delim << values, delim = ", "));
  cout << '\n';
}

inline void solve() {
  int n, k;
  cin >> n >> k;
  cout << max(0, (k - 1) / 2) << '\n';
}

int main() {
  // freopen("calc.in", "r", stdin);
  // freopen("in.txt", "w", stdout);
  cin.tie(0)->sync_with_stdio(0);
  int T = 1;
  cin >> T;
  while(T--) {
    solve();
  }
}