prepare (1/3): 
finished

make (2/3): 
clang++ -c -std=c++11 -O2 main.cpp
main.cpp:27:5: error: use of undeclared identifier 'max_edge'
} e[max_edge*2];
    ^
1 error generated.
Makefile:7: recipe for target 'main.o' failed
make: *** [main.o] Error 1

build failed