foo.cc: In function 'int main()':
foo.cc:21:11: warning: right operand of comma operator has no effect [-Wunused-value]
   21 |  for(i=N,i>=2;i--)
      |          ~^~~
foo.cc:21:18: error: expected ';' before ')' token
   21 |  for(i=N,i>=2;i--)
      |                  ^
      |                  ;

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