#include <iostream>
#include <valarray>
#include <cmath>

using namespace std;

int main(){
  
  valarray<double> v1 = {0., 1.};
  valarray<double> v2 = {1., 1.};
  valarray<double> v1_2, v2_2;
  float iloczyn, theta, absv1, absv2;
  v1_2 = pow(v1, 2.);
  v2_2 = pow(v2, 2.);
  if(v1_2.sum() == 0 && v2_2.sum() == 0){
    cout<<"Zla dlugosc wektora"<<endl;
    return 1;
  }
  absv1=sqrt(v1_2.sum());
  absv2=sqrt(v2_2.sum());
  iloczyn = (v1*v2).sum();//v1[0]*v2[0] + v1[1]*v2[1];
  theta = acos(iloczyn/(absv1*absv2));
  
  cout<<theta<<"  "<<M_PI/4<<endl;
  
  return 0;
}