const
  g=10;e=1E-5;
var
  H,s1,v,l,k,t1,t2,Vmin,Vmax:real;
  n2,n1,num,n:integer;
begin
  assign(input,'freefaller.in');reset(input);
  assign(output,'freefaller.out');rewrite(output);
  readln(h,s1,v,l,k,n);
  num:=-1;t1:=sqrt(2*h/g);
  if h<=k+e then t2:=0 else t2:=sqrt(2*(h-k-e)/g);
  if s1-v*t2+L+e<0  then num:=0 else n2:=trunc(s1-v*t2+L+e);
  if n2>n-1 then n2:=n-1;
  if s1-v*t1-e<=0 then n1:=0 else if s1-v*t1-e>n-1 then num:=0
  else if (s1-v*t1-e)=trunc(s1-v*t1-e)
  then n1:=trunc(s1-v*t1-e) else n1:=trunc(s1-v*t1-e)+1;
  if num=-1 then num:=n2-n1+1;
  writeln(num);
  close(input);close(output);
end.