foo.cc: In function ‘int main()’:
foo.cc:5:5: error: ‘scanf’ was not declared in this scope
    5 |     scanf("%lld%lld",&a,&b);
      |     ^~~~~
foo.cc:12:5: error: ‘write’ was not declared in this scope
   12 |     write(j);
      |     ^~~~~
foo.cc:3:23: warning: unused variable ‘c’ [-Wunused-variable]
    3 |     long long int a,b,c,d=0;
      |                       ^