#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace std;
using namespace __gnu_pbds;

#define int long long
#define pb push_back
#define all(s) s.begin(),s.end()
#define rall(s) s.rbegin(),s.rend()
#define pii pair<int,int>
#define fr first
#define sc second
#define bst ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
#define endl "\n"
#define no cout << "NO" << endl;
#define yes cout << "YES" << endl;
typedef tree<int,null_type,less<int>,rb_tree_tag,tree_order_statistics_node_update> ordered_set;

const int N = 5e5 + 10, mod = 1e9 + 7, inf = 1e18 + 7, logn = 23;
const double pi = acos(-1);

int bpow(int a, int n) {
	int res = 1;
	while(n) {
		if(n & 1) {
			res *= a;
		}
		n/=2;
		a *= a;
	}
	return res;
}

void solve() {
	//soln
	int n, s;
	cin >> n >> s;
	vector<int> a;
	int tmp = n;
	while(n > 0) {
		a.pb(n % 10);
		n /= 10;
	}
	n = tmp;
	if(accumulate(all(a), 0) <= s) {
		cout << 0 << endl;
		return;
	}
	reverse(all(a));
	int pref = 0;
	int pos = 0;
	for(int i = 0; i < a.size(); i++) {
		pref += a[i];
		if(pref > s) {
			pos = i;
			break;
		}
 	}
 	int ans = 0;
 	pos = a.size() - pos;
 	while(pref > s && pos <= 20) {
 		int pw = bpow(10, pos - 1);
 		int cur = (int)(n / pw) % 10;
 		pref -=	(cur - 1);
		ans += (int)(bpow(10, pos - 1) - (n % pw));
		ans += (10 - cur - 1) * pw;
		n += bpow(10, pos);
 		n -= n % bpow(10, pos);
 		pos++;
 	}
 	cout << ans << endl;
}

main() {
	bst;
	int t = 1;
	cin >> t;
	while(t--) {
		solve();
	}
}