1 Program poj2891;
  2
  3 var m:int64;
  4
  5     a,r:array[1..30000000]of int64;
  6
  7     ans,x,y,lcm:int64;
  8
  9
 10  Procedure init;
 11
 12  var i,j:longint;
 13
 14   begin
 15
 16        m:=0;
 17
 18        readln(m);
 19
 20        for i:=1 to m do
 21
 22          readln(a[i],r[i]);
 23
 24   end;
 25
 26
 27  Function extended_gcd(a,b:int64;var x,y:int64):int64;
 28
 29  var k:int64;
 30
 31   begin
 32
 33       if b=0 then begin
 34
 35                      extended_gcd:=a;
 36
 37                      x:=1;y:=0;
 38
 39                   end
 40
 41              else begin
 42
 43                      extended_gcd:=extended_gcd(b,a mod b,x,y);
 44
 45                      k:=x;x:=y;y:=k-(a div b)*y;
 46
 47                   end;
 48
 49   end;
 50
 51
 52  Procedure print(ans:int64);
 53
 54   begin
 55
 56      writeln(ans);
 57
 58   end;
 59
 60
 61  Procedure main;
 62
 63  var i:longint;
 64
 65      d,ai,ri,k:int64;
 66
 67   begin
 68
 69      ans:=0;
 70
 71      ai:=a[1];ri:=r[1];
 72
 73      for i:=2 to m do
 74
 75       begin
 76
 77           d:=extended_gcd(ai,a[i],x,y);
 78
 79           lcm:=a[i]*ai div d;
 80
 81           if (r[i]-ri)mod d<>0 then begin print(-1);exit;end;
 82
 83           k:=((x mod a[i])*(r[i]-ri) mod a[i])div d;  //这个取余很重要，没有的话就会溢出，在这wa了好久
 84
 85           ri:=((ri+ai*k) mod lcm+lcm)mod lcm;
 86
 87           ai:=lcm;
 88
 89       end;
 90
 91      print(ri);
 92
 93   end;
 94
 95
 96 Begin
 97
 98     assign(input,'input.in');reset(input);
 99
100     assign(output,'output.out');rewrite(output);
101
102          while not(eof) do
103
104           begin
105
106              init;
107
108              if m<>0 then main;
109
110           end;
111
112     close(Input);close(Output);
113
114 end.