foo.cc:1:19: warning: extra tokens at end of #include directive
 #include <cstdio> include <iostream> include <cmath>
                   ^~~~~~~
foo.cc: In function 'void prep()':
foo.cc:14:6: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
 scanf("%d",&n);
 ~~~~~^~~~~~~~~
foo.cc:17:6: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
 scanf("%d",&B[forn]);
 ~~~~~^~~~~~~~~~~~~~~

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