/in/foo.cc: In function 'int main()':
/in/foo.cc:51:32: warning: format '%lld' expects argument of type 'long long int', but argument 2 has type 'std::vector<std::pair<int, int> >::size_type {aka long unsigned int}' [-Wformat=]
     printf("%lld\n", ans.size());
                                ^