let n, m, a = Scanf.scanf "%d %d %d" (fun x y z -> x, y, z);;

let g = Array.make (n+1) [];;
for i = 1 to m do
  let l, r, p = Scanf.scanf " %d %d %d" (fun x y z -> x-1, y, z) in
  g.(l) <- (r,p)::g.(l);
done;;

let inf = max_int / 4;;
let dp1 = Array.make (n+1) (-inf);;
let dp2 = Array.make (n+1) (-inf);;
dp1.(0) <- 0;;
for i = 0 to n-1 do
  dp2.(i+1) <- max dp2.(i+1) dp1.(i);
  dp2.(i+1) <- max dp2.(i+1) dp2.(i);
  List.iter (fun (r, p) ->
      dp1.(r) <- max dp1.(r) (dp1.(i) + p - a);
      dp1.(r) <- max dp1.(r) (dp2.(i) + p - a*2);
    ) g.(i);
done;;

Printf.printf "%d\n" (max (dp1.(n)+a) dp2.(n));;