foo.cc: In function 'int main()':
foo.cc:18:12: warning: unused variable 'a' [-Wunused-variable]
  int n,r,m,a;
            ^
foo.cc: In function 'int gcd(int, int)':
foo.cc:15:1: warning: control reaches end of non-void function [-Wreturn-type]
 }
 ^

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