diff --git a/quad10/fenomens/lab/p4/Makefile b/quad10/fenomens/lab/p4/Makefile
index 21e5cbf..9c7b58a 100644
--- a/quad10/fenomens/lab/p4/Makefile
+++ b/quad10/fenomens/lab/p4/Makefile
@@ -2,9 +2,11 @@
 FC=gfortran
 FC_FLAGS=-O3 -Wall #-g -fbacktrace -fcheck=all
 
-all: MC-2.o
+all: MC-2.o out/cv_via_derivative
 make_out_folder:
 	mkdir -p out data_out
+out/cv_via_derivative: cv_via_derivative.cc
+	g++ cv_via_derivative.cc -Wall -o out/cv_via_derivative
 MC-2.o: make_out_folder mt19937ar.o generateSpinMatrix.o magne.o energ.o pbc.o writeconfig.o MC-2.f90
 	$(FC) $(FC_FLAGS) -c MC-2.f90
 	$(FC) $(FC_FLAGS) MC-2.o generateSpinMatrix.o mt19937ar.o magne.o energ.o pbc.o writeconfig.o -o out/mc2