#include <bits/stdc++.h>
using namespace std;
const int maxn = 2e5 + 7;
const int mod = 1e9 + 7;
const double eps = 1e-15;
const double pi = acos(-1);
const int INF = 0x3f3f3f;
long long read() {
  long long c = getchar(), Nig = 1, x = 0;
  while (!isdigit(c) && c != '-') c = getchar();
  if (c == '-') Nig = -1, c = getchar();
  while (isdigit(c)) x = ((x << 1) + (x << 3)) + (c ^ '0'), c = getchar();
  return Nig * x;
}
long long gcd(long long a, long long b) { return b == 0 ? a : gcd(b, a % b); }
int main() {
  int t;
  scanf("%d", &t);
  while (t--) {
    int n, k;
    scanf("%d%d", &n, &k);
    int ans;
    if (n % k == 0)
      ans = n;
    else
      ans = (n / k) * k, ans += min(n % k, k / 2);
    cout << ans << '\n';
  }
}
