phi

int Phi(int n)
{
  int d,p;
  double phi;
  phi = n;
  d = 2;
  while(n != 1)
  {
    p = 0;
    while (n % d ==0)
    {
      p++;
      n/=d;
    }
    if(p > 0) phi *= (d-1) * 1./d;
    if(d * d < n) d ++;
    else d = n;
  }
  return int(phi);
}