foo.cc: In function ‘void dts::main()’:
foo.cc:20:9: error: ‘scanf’ was not declared in this scope
   20 | while (~scanf("%lld%lld",&a,&b))
      |         ^~~~~
foo.cc:21:1: error: ‘printf’ was not declared in this scope
   21 | printf("%lld\n",a+b-gcd(a,b));
      | ^~~~~~
foo.cc:2:1: note: ‘printf’ is defined in header ‘<cstdio>’; this is probably fixable by adding ‘#include <cstdio>’
    1 | #include <cmath>
  +++ |+#include <cstdio>
    2 | using namespace std;