makefile found - problem

[Shaharak88]

i installed pangolin 0.5 but when i run:
cd ORB_SLAM2
chmod +x build.sh
./build.sh
i get:
make: *** No targets specified and no makefile found. Stop.
do you know what is the problem?
i tried to remove and re-build couple of times but it didnt work.
what should i do?