Compilare: user.cpp: In function ‘int main()’: user.cpp:21:38: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("fractii.in", "r", stdin); ^ user.cpp:22:40: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("fractii.out", "w", stdout); ^ user.cpp: In function ‘void sieve()’: user.cpp:10:23: warning: iteration 1000006u invokes undefined behavior [-Waggressive-loop-optimizations] phi[i] = i - 1; ^ user.cpp:9:23: note: containing loop for (int i = 1; i <= maxn; i++) { ^