/in/foo.cc: In function 'void dfs(int, int)':
/in/foo.cc:27:14: error: 'start' was not declared in this scope
  if(finish - start > 900000) return;
              ^~~~~
/in/foo.cc: In function 'int main()':
/in/foo.cc:45:10: warning: unused variable 'start' [-Wunused-variable]
  clock_t start = clock();
          ^~~~~