var n:longint;



 procedure citire;
 var i,s,a,b,c:longint;
 begin

  readln(n); s:=0;

  if n=2 then begin
        readln(a,b);
        s:=s+b;
        readln(a,b);
        s:=s+b;
        end
  else
  for i:=1 to n do
        begin
         readln(a,b,c);

         if (i=1) or (i=n) then s:=s+a
                else s:=s+c;
        end;

  writeln(s);
 end;


begin
 citire;
end.