program ph;
var
        f:text;
        a:array[1..2,1..50000]of longint;
        i,j,m,k,l,n,r,u,max,maxn,p,x,y,h:longint;
begin
        for i:=1 to 50000 do
        begin
                a[1,i]:=-1;
                a[2,i]:=i;
        end;
        assign(f,'balance.in');
        reset(f);
        readln(f,n);
        for i:=1 to n do
        begin
                readln(f,x,y);
                a[1,y]:=x;
                a[2,y]:=y;
                if y>h then h:=y;
        end;
        close(f);
        l:=0;
        m:=0;
        max:=0;
        maxn:=0;
        for i:=1 to h do
        for j:=1 to h do
        begin
                for k:=i to j do
                begin
                        if a[1,k]=0 then
                        begin
                                if p <> 1 then u:=k;
                                p:=1;
                                l:=l+1;
                        end;
                        if a[1,k]=1 then
                        begin
                                m:=m+1;
                                r:=k;
                        end;
                        if (m=l) and(m<>0) then
                        begin
                                if r>u then max:=r-u
                                else max:=u-r;
                                if maxn<max then maxn:=max;
                        end;
                end;
                m:=0;
                l:=0;
        end;
        assign(f,'balance.out');
        rewrite(f);
        writeln(f,maxn);
        close(f);
end.