output_description: Print an integer representing the minimum number of times Takahashi will press
  the buttons.
  
  * * *
input_description: The input is given from Standard Input in the following format:
  
      
      
      N
      A_1 B_1
      :
      A_N B_N
attempt: # coding: utf-8
  import re
  import math
  from collections import defaultdict
  from collections import deque
  import collections
  from fractions import Fraction
  import itertools
  from copy import deepcopy
  import random
  import time
  import os
  import queue
  import sys
  import datetime
  from functools import lru_cache
  
  # @lru_cache(maxsize=None)
  readline = sys.stdin.readline
  sys.setrecursionlimit(2000000)
  # import numpy as np
  alphabet = "abcdefghijklmnopqrstuvwxyz"
  mod = int(10**9 + 7)
  inf = int(10**20)
  
  
  def yn(b):
      if b:
          print("yes")
      else:
          print("no")
  
  
  def Yn(b):
      if b:
          print("Yes")
      else:
          print("No")
  
  
  def YN(b):
      if b:
          print("YES")
      else:
          print("NO")
  
  
  class union_find:
      def __init__(self, n):
          self.n = n
          self.P = [a for a in range(n)]
          self.rank = [0] * n
  
      def find(self, x):
          if x != self.P[x]:
              self.P[x] = self.find(self.P[x])
          return self.P[x]
  
      def same(self, x, y):
          return self.find(x) == self.find(y)
  
      def link(self, x, y):
          if self.rank[x] < self.rank[y]:
              self.P[x] = y
          elif self.rank[y] < self.rank[x]:
              self.P[y] = x
          else:
              self.P[x] = y
              self.rank[y] += 1
  
      def unite(self, x, y):
          self.link(self.find(x), self.find(y))
  
      def size(self):
          S = set()
          for a in range(self.n):
              S.add(self.find(a))
          return len(S)
  
  
  def ispow(a, b):  # aはbの累乗数か
      now = b
      while now < a:
          now *= b
      if now == a:
          return True
      else:
          return False
  
  
  def getbin(num, size):
      A = [0] * size
      for a in range(size):
          if (num >> (size - a - 1)) & 1 == 1:
              A[a] = 1
          else:
              A[a] = 0
      return A
  
  
  def getfacs(n, mod_=0):
      A = [1] * (n + 1)
      for a in range(2, len(A)):
          A[a] = A[a - 1] * a
          if mod_ > 0:
              A[a] %= mod_
      return A
  
  
  def comb(n, r, mod, fac):
      if n - r < 0:
          return 0
      return (fac[n] * pow(fac[n - r], mod - 2, mod) * pow(fac[r], mod - 2, mod)) % mod
  
  
  def nextcomb(num, size):
      x = num & (-num)
      y = num + x
      z = num & (~y)
      z //= x
      z = z >> 1
      num = y | z
      if num >= (1 << size):
          return False
      else:
          return num
  
  
  def getprimes(n, type="int"):
      if n == 0:
          if type == "int":
              return []
          else:
              return [False]
      A = [True] * (n + 1)
      A[0] = False
      A[1] = False
      for a in range(2, n + 1):
          if A[a]:
              for b in range(a * 2, n + 1, a):
                  A[b] = False
      if type == "bool":
          return A
      B = []
      for a in range(n + 1):
          if A[a]:
              B.append(a)
      return B
  
  
  def isprime(num):
      if num <= 1:
          return False
      i = 2
      while i * i <= num:
          if num % i == 0:
              return False
          i += 1
      return True
  
  
  def ifelse(a, b, c):
      if a:
          return b
      else:
          return c
  
  
  def join(A, c=""):
      n = len(A)
      A = list(map(str, A))
      s = ""
      for a in range(n):
          s += A[a]
          if a < n - 1:
              s += c
      return s
  
  
  def factorize(n, type_="dict"):
      b = 2
      list_ = []
      while b * b <= n:
          while n % b == 0:
              n //= b
              list_.append(b)
          b += 1
      if n > 1:
          list_.append(n)
      if type_ == "dict":
          dic = {}
          for a in list_:
              if a in dic:
                  dic[a] += 1
              else:
                  dic[a] = 1
          return dic
      elif type_ == "list":
          return list_
      else:
          return None
  
  
  def pm(x):
      return x // abs(x)
  
  
  def inputintlist():
      return list(map(int, input().split()))
  
  
  ######################################################################################################
  
  n = int(input())
  A = [0] * n
  B = [0] * n
  for a in range(n):
      A[a], B[a] = inputintlist()
  ans = 0
  R = [0] * n
  for a in range(n - 1, -1, -1):
      r = 0
      if a != n - 1:
          r = R[a + 1]
      num = ((A[a] + r + B[a] - 1) // B[a]) * B[a] - A[a] - r
      R[a] = num + r
  print(R[0])
  
problem_description: Statement
  
  There are an integer sequence A_1,...,A_N consisting of N terms, and N
  buttons. When the i-th (1 ≦ i ≦ N) button is pressed, the values of the i
  terms from the first through the i-th are all incremented by 1.
  
  There is also another integer sequence B_1,...,B_N. Takahashi will push the
  buttons some number of times so that for every i, A_i will be a multiple of
  B_i.
  
  Find the minimum number of times Takahashi will press the buttons.
samples: [{"input": "3\n    3 5\n    2 7\n    9 4", "output": "7\n    \n\nPress the first button twice, the second button twice and the third button\nthree times.\n\n* * *"}, {"input": "7\n    3 1\n    4 1\n    5 9\n    2 6\n    5 3\n    5 8\n    9 7", "output": "22"}]