A.cpp

//#pragma GCC optimize "trapv"
#include<bits/stdc++.h>
#define ll long long 
#define fab(a,b,i) for(int i=a;i<b;i++)
#define pb push_back
#define db double
#define mp make_pair
#define endl "\n"
#define f first
#define se second
#define all(x) x.begin(),x.end()
#define MOD 1000000007
#define quick ios_base::sync_with_stdio(false);cin.tie(NULL)
using namespace std;
vector<ll int > v;
void printDivisors(int n) 
{ 
    // Note that this loop runs till square root 
    for (int i=1; i<=sqrt(n); i++) 
    { 
        if (n%i == 0) 
        { 
            // If divisors are equal, print only one 
            if (n/i == i) 
                v.pb(i); 
  
            else // Otherwise print both 
                {
                	v.pb(i);
                	v.pb(n/i);
                } 
        } 
    } 
}
int main()
{ quick;
#ifndef ONLINE_JUDGE
    freopen("input.txt", "r", stdin);
    freopen("output.txt", "w", stdout);
#endif
	int t;
	cin>>t;
	while(t--)
	{
		ll int a,b;
		cin>>a>>b;
		//if()
		ll int ans=a%b;
		if(a%b==0)
			cout<<0<<endl;
		else
			
		cout<<b-ans<<endl;

	}
	

	return 0;
}