program balance;
type
        rec=record
        id,x:longint;
        end;
var
        n,i,j,ans:longint;
        data:array[1..50000]of rec;
        f:array[0..50000]of longint;
procedure swap(var a,b:rec);
var
        t:rec;
begin
        t:=a;
        a:=b;
        b:=t;
end;
procedure qsort(l,r:longint);
  var i,j,mid:longint;
  begin
    i:=l;j:=r; mid:=data[(l+r) div 2].x;
  repeat
    while data[i].x<mid do inc(i);
    while data[j].x>mid do dec(j);
    if i<=j then begin
    swap(data[i],data[j]);
    inc(i);dec(j);
    end;
  until i>j;
  if l<j then qsort(l,j);
  if i<r then qsort(i,r);
end;{sort}
procedure init;
begin
        assign(input,'balance.in');
        reset(input);
        assign(output,'balance.out');
        rewrite(output);
        readln(n);
        for i:=1 to n do
        begin
                readln(data[i].id,data[i].x);

        end;
        qsort(1,n);
        f[0]:=0;
        if data[1].id=1 then f[1]:=1 else f[1]:=0;
        for i:=2 to n do
         begin
         f[i]:=f[i-1]+data[i].id;
         end;
end;
procedure closef;
begin
        close(input);
        close(output);
end;
procedure main;
begin
        ans:=-1;
        for i:=1 to n do
         for j:=i to n do
           begin
               if f[j]-f[i-1]=(j-i+1)-(f[j]-f[i-1]) then
               if data[j].x-data[i].x>ans then
                ans:=data[j].x-data[i].x;
           end;
        writeln(ans);

end;
begin
        init;
        main;
        closef;
end.