books.cpp: In function 'long long int minimum_walk(std::vector<int>, int)':
books.cpp:21:11: warning: unused variable 'b' [-Wunused-variable]
int a,b,c,d,i,j,k;
^
books.cpp:21:13: warning: unused variable 'c' [-Wunused-variable]
int a,b,c,d,i,j,k;
^
books.cpp:21:15: warning: unused variable 'd' [-Wunused-variable]
int a,b,c,d,i,j,k;
^
books.cpp:21:19: warning: unused variable 'j' [-Wunused-variable]
int a,b,c,d,i,j,k;
^
books.cpp:21:21: warning: unused variable 'k' [-Wunused-variable]
int a,b,c,d,i,j,k;
^
/tmp/ccWFWvL5.o: In function `main':
grader.cpp:(.text.startup+0x0): multiple definition of `main'
/tmp/ccxFrpl7.o:books.cpp:(.text.startup+0x0): first defined here
collect2: error: ld returned 1 exit status