Compilare: user.cpp: In function ‘long long int f(int)’: user.cpp:17:17: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (j=1;j<=n;++j) ^ user.cpp:20:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while (M.size() > k) ^ user.cpp: In function ‘int main()’: user.cpp:36:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i=1;i<=n;++i) ^