/in/foo.cc: In function 'int main()':
/in/foo.cc:38:21: warning: format '%lf' expects argument of type 'double', but argument 2 has type 'll' {aka 'long long int'} [-Wformat=]
   38 |         printf("%.6lf",1/(1/n+1/m));
      |                 ~~~~^  ~~~~~~~~~~~
      |                     |   |
      |                     |   ll {aka long long int}
      |                     double
      |                 %.6lld