Compilare: main.cpp: In function 'int main()': main.cpp:2:92: warning: statement has no effect [-Wunused-value] std::ifstream i("tg.in");std::ofstream t("tg.out");bool s[4000009];int main(){int n,j,i=1;i>>n;int a=0;for(;i<=n;++i)if(!s[i])for(j=1;j*j*i<=n;++j)s[j*j*i]=1,a+=j-1;t<<a;} ~^~~ main.cpp:2:110: warning: 'n' is used uninitialized in this function [-Wuninitialized] std::ifstream i("tg.in");std::ofstream t("tg.out");bool s[4000009];int main(){int n,j,i=1;i>>n;int a=0;for(;i<=n;++i)if(!s[i])for(j=1;j*j*i<=n;++j)s[j*j*i]=1,a+=j-1;t<<a;} ~^~~