#include <bits/stdc++.h>
using namespace std;
long long int mod = 1e9 + 7;
const long long int N = 1e6 + 5;
long long int fact[N + 2];
long long int spf[N];
void sieve() {
  spf[1] = 1;
  for (long long int i = 2; i < N; i++) {
    spf[i] = i;
  }
  for (long long int i = 4; i < N; i += 2) {
    spf[i] = 2;
  }
  for (long long int i = 3; i * i < N; i++) {
    if (spf[i] == i) {
      for (long long int j = i * i; j < N; j += i) {
        if (spf[j] == j) {
          spf[j] = i;
        }
      }
    }
  }
}
long long int mp[N + 1];
void getfacots(long long int x) {
  long long int cnt = 0;
  while (x != 1) {
    mp[spf[x]]++;
    x = x / spf[x];
  }
}
long long int modexp(long long int x, long long int y, long long int p) {
  if (x == 0) {
    return 0;
  }
  if (y == 0) {
    return 1;
  }
  if (y % 2 == 0) {
    long long int res = modexp(x, y / 2, p);
    return (res * res) % p;
  } else {
    long long int res = modexp(x, y - 1, p);
    return (x * res) % p;
  }
}
long long int inverse(long long int n, long long int p) {
  return modexp(n, p - 2, p);
}
long long int ncr(long long int n, long long int r, long long int mod) {
  long long int ans = ((fact[n] % mod * inverse(fact[r], mod) % mod) % mod *
                       inverse(fact[n - r], mod) % mod) %
                      mod;
  return ans;
}
signed main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  long long int t;
  cin >> t;
  while (t--) {
    long long int n, m;
    cin >> n >> m;
    long long int ans;
    long long int r = n % m;
    long long int x = n / m;
    if (r > m / 2) {
      cout << x * m + m / 2 << endl;
    } else {
      cout << n << endl;
    }
  }
  return 0;
}
