{灯
 哈希表
 Author: yangbohua
 Time: 2010-11-16 09:09}

program light;
var
  f:array[0..20000000] of boolean;
  n,i,j,p,t:longint;
  a,q:double;
begin
  assign(input,'light.in');
  reset(input);
  assign(output,'light.out');
  rewrite(output);
  readln(n);
  fillchar(f,sizeof(f),false);
  for i:=1 to n do
  begin
    readln(a,t);
    q:=0;
    for j:=1 to t do
    begin
      q:=q+a;
      p:=trunc(q);
      if f[p]
        then f[p]:=false
        else f[p]:=true;
    end;
  end;
  i:=1;
  while f[i]=false do
    inc(i);
  writeln(i);
  close(input);
  close(output);
end.