/in/foo.cc: In function 'int main()':
/in/foo.cc:31:8: warning: variable 'l' set but not used [-Wunused-but-set-variable]
  lon N,l;
        ^
/in/foo.cc:39:6: warning: unused variable 'top' [-Wunused-variable]
  int top=49,cnt=0;
      ^~~