using System;
using System.Collections.Generic;
using System.Text;
using System.Linq;

namespace MSL001
{
    //public class A
    //{

    //    public static void Main(string[] args)
    //    {

    //        var c = new ConsoleInput(Console.In);
    //        var S = c.Read;
    //        var A = c.ReadLong;
    //        var B = c.ReadLong;
    //        var C = c.ReadLong;
    //        var D = c.ReadLong;
    //        var sb = new StringBuilder(S.Length + 10);

    //        for (int i = 0; i < S.Length; i++)
    //        {
    //            if(i == A || i == B || i == C || i == D)
    //            {
    //                sb.Append("\"");
    //            }
    //            sb.Append(S[i]);
    //        }
    //        if (D == S.Length) sb.Append("\"");
    //        Console.WriteLine(sb.ToString());
    //    }


    //}

    //public class B
    //{
    //    public static void Main(string[] args)
    //    {
    //        var c = new ConsoleInput(Console.In);
    //        Dictionary<string, long> dic = new Dictionary<string, long>();
    //        var N = c.ReadLong;
    //        for (int i = 0; i < N; i++)
    //        {
    //            string k = c.Read;
    //            if(dic.TryGetValue(k,out long value))
    //            {
    //                dic[k] = value + 1;
    //            }
    //            else{
    //                dic.Add(k, 1);
    //            }
    //        }
    //        var M = c.ReadLong;
    //        for (int i = 0; i < M; i++)
    //        {
    //            string k = c.Read;
    //            if(dic.TryGetValue(k,out long value))
    //            {
    //                dic[k] = value - 1;
    //            }
    //        }

    //        long max = dic.Values.Max();
    //        Console.WriteLine(max > 0 ? max : 0);

    //    }

    //}


    public class C
    {
        public static void Main(string[] args)
        {
            var c = new ConsoleInput(Console.In);
            var N = c.ReadInt;
            var A = new long[N];
            var B = new long[N];
            for (int i = 0; i < N; i++)
            {
                A[i] = c.ReadLong;
                B[i] = c.ReadLong;
            }

            long count = 0;
            for (int i = N - 1; i >= 0; i--)
            {
                long diff = B[i] - ((A[i] + count) % B[i]);
                if (diff == B[i]) diff = 0;
                count += diff;
            }
            Console.WriteLine(count);

        }
    }
    public class ConsoleInput
    {
        private readonly System.IO.TextReader _stream;
        private char _separator = ' ';
        private Queue<string> inputStream;
        public ConsoleInput(System.IO.TextReader stream, char separator = ' ')
        {
            this._separator = separator;
            this._stream = stream;
            inputStream = new Queue<string>();
        }
        public string Read
        {
            get
            {
                if (inputStream.Count != 0) return inputStream.Dequeue();
                string[] tmp = _stream.ReadLine().Trim().Split(_separator);
                for (int i = 0; i < tmp.Length; ++i)
                    inputStream.Enqueue(tmp[i].Trim());
                return inputStream.Dequeue();
            }
        }
        public string ReadLine { get { return _stream.ReadLine(); } }
        public int ReadInt { get { return int.Parse(Read); } }
        public long ReadLong { get { return long.Parse(Read); } }
        public double ReadDouble { get { return double.Parse(Read); } }
        public string[] ReadStrArray(long N) { var ret = new string[N]; for (long i = 0; i < N; ++i) ret[i] = Read; return ret; }
        public int[] ReadIntArray(long N) { var ret = new int[N]; for (long i = 0; i < N; ++i) ret[i] = ReadInt; return ret; }
        public long[] ReadLongArray(long N) { var ret = new long[N]; for (long i = 0; i < N; ++i) ret[i] = ReadLong; return ret; }
    }
}

Measured memory_bytes: 47876