tong chu so

#include <bits/stdc++.h>

#define ll long long
#define pb push_back
#define pii pair<int, int>
#define pll pair<ll, ll>
#define el endl
#define umi unordered_map<int, int>
#define umll unordered_map<ll, ll>
#define all(vect) vect.begin(), vect.end()
#define reset(A) memset(A, 0, sizeof(A))
#define approx(n) fixed << setprecision(n)

using namespace std;

const int mod = 1e9 + 7;

ll sumOfDigits(ll n) {
    ll sum = 0;
    while(n) {
        sum += n % 10;
        n /= 10;
    }
    return sum;
}

void solve()
{
  ll n, s;
  cin >> n >> s;
  if(sumOfDigits(n) <= s)
  {
    cout << 0 << el;
    return;
  }
  int i = 1;
  ll p = (ll)pow(10, 1);
  while(p < n) {
    i++;
    p = (ll)pow(10, i);
  }
  if(i % 2 == 0) {
    p++;
  }
  // cout << p - n << el;
  p -= n;
  ll ind = 1;
  while(true) {
    ll te = (ll)pow(10, ind);
    if(sumOfDigits(n + p % te) <= s) {
      cout << p % te << el;
      return;
    }
    ind++;
  }
}

int main()
{
  int t = 1;
  cin >> t;
  // cin.ignore();
  while (t--)
  {
    solve();
  }
  return 0;
}