Outside declaration of botan path

Makefile

@@ -1,6 +1,7 @@
 CXX = g++
-CXXFLAGS = -std=c++17 -I/usr/local/include/botan-2/ -lbotan-2
+CXXFLAGS = -std=c++17 -lbotan-2
 RUN = ./
+BOTAN_PATH = /usr/local/include/botan-2/
 LD_LIBRARY_PATH = /usr/local/lib
 
 .PHONY: all clean build run
@@ -8,7 +9,7 @@ LD_LIBRARY_PATH = /usr/local/lib
 all: build run
 
 build: example.cpp
-	$(CXX) example.cpp $(CXXFLAGS) -o example
+	$(CXX) example.cpp $(CXXFLAGS) -I$(BOTAN_PATH) -o example
 run:
 	$(RUN)example