foo.cc: In function 'int main()':
foo.cc:15:30: error: no matching function for call to '__gcd(long long int&, int&)'
   mul = mul / __gcd(mul, b[i]) * b[i];
                              ^
In file included from /usr/include/c++/7/algorithm:62:0,
                 from /usr/include/x86_64-linux-gnu/c++/7/bits/stdc++.h:65,
                 from foo.cc:1:
/usr/include/c++/7/bits/stl_algo.h:1232:5: note: candidate: template<class _EuclideanRingElement> _EuclideanRingElement std::__gcd(_EuclideanRingElement, _EuclideanRingElement)
     __gcd(_EuclideanRingElement __m, _EuclideanRingElement __n)
     ^~~~~
/usr/include/c++/7/bits/stl_algo.h:1232:5: note:   template argument deduction/substitution failed:
foo.cc:15:30: note:   deduced conflicting types for parameter '_EuclideanRingElement' ('long long int' and 'int')
   mul = mul / __gcd(mul, b[i]) * b[i];
                              ^
foo.cc:8:7: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
  scanf("%d", &n);
  ~~~~~^~~~~~~~~~
foo.cc:10:8: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   scanf("%d%d", a + i, b + i);
   ~~~~~^~~~~~~~~~~~~~~~~~~~~~