Compilare: main.cpp: In function 'void go(int, std::pair<int, int>)': main.cpp:48:14: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if (step == primes.size ()) { ~~~~~^~~~~~~~~~~~~~~~~ main.cpp: In function 'int main()': main.cpp:57:40: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result] freopen ("tenerife.in", "r", stdin); ^ main.cpp:58:42: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result] freopen ("tenerife.out", "w", stdout); ^