#include <bits/stdc++.h>
using namespace std;
inline long long read() {
  long long x = 0;
  char ch = getchar();
  bool d = 1;
  for (; !isdigit(ch); ch = getchar())
    if (ch == '-') d = 0;
  for (; isdigit(ch); ch = getchar()) x = x * 10 + ch - '0';
  return d ? x : -x;
}
inline void write(long long x) {
  if (x < 0) x = -x, putchar('-');
  if (x >= 10) write(x / 10);
  putchar('0' + x % 10);
}
inline void writeln(long long x) {
  write(x);
  puts("");
}
inline void writep(long long x) {
  write(x);
  putchar(' ');
}
inline unsigned long long rnd() {
  return ((unsigned long long)rand() << 30 ^ rand()) << 4 | rand() % 4;
}
int main() {
  int T = read();
  while (T--) {
    int a = read(), b = read(), c = a / b;
    if (a % b == 0)
      puts("0");
    else
      writeln((c + 1) * b - a);
  }
}
