const maxn=;

 type

   link=^node;

   node=record

     t,d:longint;

     f:link;

   end;

 var n,m,s,i,j,u,v,w,max:longint;

 adj:array[..] of link;

 f:array[..] of longint;

 d,val:array[..] of longint;

 went:array[..] of boolean;

 procedure insert(f,t,d:longint);

 var p:link;

 begin

   new(p);

   p^.f:=adj[f];

   p^.t:=t;

   p^.d:=d;

   adj[f]:=p;

 end;

 procedure spfa(s:longint);

 var l,r,now,i:longint;

 p:link;

 begin

   for i:= to n do

     d[i]:=maxn;

   fillchar(went,sizeof(went),true);

   l:=; r:=; f[]:=s; d[s]:=; went[s]:=false;

   while l<=r do

     begin

       now:=f[l];

       p:=adj[now];

       while p<>nil do

         begin

           if d[p^.t]>d[now]+p^.d then

             begin

               d[p^.t]:=d[now]+p^.d;

               if went[p^.t] then

                 begin

                   went[p^.t]:=false;

                   inc(r);

                   f[r]:=p^.t;

                 end;

             end;

           p:=p^.f;

         end;

       went[now]:=true;

       inc(l);

     end;

 end;

 begin

   readln(n,m,s);

   for i:= to m do

     begin

       readln(u,v,w);

       insert(u,v,w);

       //insert(v,u,w);

     end;

   for i:= to n do

     begin

       spfa(i);

       val[i]:=d[s];

       //writeln(sb);

       //writeln(d[s]);

     end;

   spfa(s);

   for i:= to n do

     //if i<>s then

       begin

         inc(val[i],d[i]);

         if val[i]>max then max:=val[i];

       end;

   writeln(max);

 end.