#include <bits/stdc++.h>
#ifdef _DEBUG
#include "debug.hpp"
#else
#define debug(...)
#endif
#define fastIO (cin.tie(0), cout.tie(0), ios::sync_with_stdio(false))
#define precise(i) fixed << setprecision(i)
using ill = int64_t;
using ull = uint64_t;
using namespace std;

void solve() {
  double px, py, qx, qy;
  cin >> px >> py >> qx >> qy;
  cout << precise(20) << (abs(px - qx) + abs(py - qy)) / 2 << '\n';
}

void wrapper() {
  int loop;
  cin >> loop;
  for (int i = 0; i < loop; i++) {
    auto start = chrono::steady_clock::now();
    cout << "[TEST " << i + 1 << "]\n";
    solve();
    auto end = chrono::steady_clock::now();
    chrono::duration<double> elapsed = end - start;
    cout << "[elapsed : " << elapsed.count() << "]" << '\n';
  }
}

int main() {
  fastIO;
#ifdef _DEBUG
  wrapper();
#else
  solve();
#endif
}