foo.cc: In function 'int sn(int)':
foo.cc:12:9: warning: 's' may be used uninitialized in this function [-Wmaybe-uninitialized]
   12 |  return s;
      |         ^
foo.cc: In function 'int main()':
foo.cc:18:33: warning: 's' may be used uninitialized in this function [-Wmaybe-uninitialized]
   18 |  if(m+3==n && sn(m)%6==0 &&sn(n)%6==0)
      |                            ~~~~~^~
foo.cc:18:20: warning: 's' may be used uninitialized in this function [-Wmaybe-uninitialized]
   18 |  if(m+3==n && sn(m)%6==0 &&sn(n)%6==0)
      |               ~~~~~^~

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