#pragma warning disable
using System;
using System.Collections;
using System.Collections.Generic;
using System.Diagnostics;
using System.IO;
using System.Linq;
using System.Numerics;
using System.Runtime.Serialization.Formatters.Binary;
using System.Text;
using System.Text.RegularExpressions;
static class MainClass
{
public static void Main(string[] args)
{
var n = Console.ReadLine().ToInt32();
var items = new List<ItemClass>();
for (int i = 0; i < n; i++)
{
var ab = Console.ReadLine().SplittedStringToInt32List();
var a = ab[0];
var b = ab[1];
var ite = new ItemClass() { A = a, B = b };
items.Add(ite);
}
var sum = 0l;
items.Reverse();
foreach (var item in items)
{
item.A += sum;
sum += item.Overs;
}
Console.WriteLine(sum);
Console.ReadLine();
}
class ItemClass
{
public long A;
public int B;
public long Rem => A % B;
public long Overs => A % B == 0 ? 0 : B - A % B;
}
#region
public static int ParentCount;
public static int[] Parents;
public static int[] IfParentsChildrenCount;
public static int[] Ranks;
public static void InitializeUnionFind(int N)
{
Parents = new int[N];
Ranks = new int[N];
IfParentsChildrenCount = new int[N];
for (int i = 0; i < N; i++)
{
Parents[i] = i;
Ranks[i] = 0;
IfParentsChildrenCount[i] = 1;
}
ParentCount = N + 1;
}
public static int Root(int a)
{
if (Parents[a] == a)
{
return a;
}
else
{
Parents[a] = Root(Parents[a]);
return Parents[a];
}
}
public static bool Same(int a, int b)
{
return Root(a) == Root(b);
}
public static void Unite(int a, int b)
{
var parentA = Root(a);
var parentB = Root(b);
if (parentA == parentB)
return;
if (Ranks[parentA] < Ranks[parentB])
{
Parents[parentA] = parentB;
IfParentsChildrenCount[parentB] += IfParentsChildrenCount[parentA];
ParentCount -= IfParentsChildrenCount[parentA];
IfParentsChildrenCount[parentA] = 0;
}
else
{
Parents[parentB] = parentA;
if (Ranks[parentA] == Ranks[parentB])
{
Ranks[parentA]++;
}
IfParentsChildrenCount[parentA] += IfParentsChildrenCount[parentB];
ParentCount -= IfParentsChildrenCount[parentB];
IfParentsChildrenCount[parentB] = 0;
}
}
#endregion
#region ライブラリ
public static long ToInt64(this string str) => long.Parse(str);
public static int ToInt32(this string str) => str == "" ? 0 : int.Parse(str);
public static BigInteger ToBigInteger(this string str) => BigInteger.Parse(str);
public static List<string> SplittedStringToList(this string str) => str.Split(new[] { ' ' }, StringSplitOptions.RemoveEmptyEntries).ToList();
public static List<int> SplittedStringToInt32List(this string str) => str.Split(new[] { ' ' }, StringSplitOptions.RemoveEmptyEntries).Select(x => int.Parse(x)).ToList();
public static List<long> SplittedStringToInt64List(this string str) => str.Split(new[] { ' ' }, StringSplitOptions.RemoveEmptyEntries).Select(x => long.Parse(x)).ToList();
public static List<BigInteger> SplittedStringToBigInteger(this string str) => str.Split(new[] { ' ' }, StringSplitOptions.RemoveEmptyEntries).Select(x => BigInteger.Parse(x)).ToList();
public const int INF = int.MaxValue / 4;
public const long LONGINF = long.MaxValue / 2;
public const int Mod1e9 = 1000000007;
public static void PrintArray(char[,] array)
{
for (int i = 0; i < array.GetLength(0); i++)
{
var sb = new StringBuilder();
for (int j = 0; j < array.GetLength(1); j++)
{
sb.Append(array[i, j]);
}
Console.WriteLine(sb.ToString());
}
}
public static int Manhattan(int x1, int x2, int y1, int y2)
{
return Math.Abs(x1 - x2) + Math.Abs(y1 - y2);
}
public static Dictionary<T, int> ToCountedDictionary<T>(this IEnumerable<T> items)
{
var dic = new Dictionary<T, int>();
foreach (var item in items)
{
if (dic.ContainsKey(item))
dic[item]++;
else
dic.Add(item, 1);
}
return dic;
}
public static Dictionary<TKey, TValue> KeyValuePairListToDictionary<TKey, TValue>(this IEnumerable<KeyValuePair<TKey, TValue>> pairs)
{
var dic = new Dictionary<TKey, TValue>();
foreach (var item in pairs)
{
dic.Add(item.Key, item.Value);
}
return dic;
}
public static long Sums(IEnumerable<int> list)
{
var sum = 0l;
foreach (var item in list)
{
sum += Math.Abs(item);
}
return sum;
#endregion
}
public static int[] dx = { -1, 1, 0, 0 };
public static int[] dy = { 0, 0, 1, -1 };
public static int[] dxx = { 0, 1, 1, 1, 0, -1, -1, -1 };
public static int[] dyy = { 1, 1, 0, -1, -1, -1, 0, 1 };
}