program bing;
var
 f1,f2:text;
 s,p:longint;
 f,fp:array[0..2500000] of longint;
procedure init;
begin
 assign(f1,'goat.in');reset(f1);
 assign(f2,'goat.out');rewrite(f2);
 readln(f1,s,p);
 fillchar(f,sizeof(f),0);
 fillchar(fp,sizeof(fp),0);
 f[0]:=0;fp[0]:=0;
end;
procedure nb;
var
 i,t,tp:longint;
begin
 t:=s;
 for i:=1 to s do
 begin
  if fp[i-1]-1<=p then
   begin
    if f[i-1]+1<t then begin t:=f[i-1]+1;tp:=fp[i-1]-1;
                               if tp<=0 then tp:=0;end;
   end;
  if (i-5>=0)and(fp[i-5]+2<=p) then
   begin
    if f[i-5]+1<t then begin t:=f[i-5]+1;tp:=fp[i-5]+2;end;
   end;
  if (i-10>=0)and(fp[i-10]+5<=p) then
   begin
    if f[i-10]+1<t then begin t:=f[i-10]+1;tp:=fp[i-10]+5;end;
   end;
  f[i]:=t;
  fp[i]:=tp;
  t:=s;
 end;
end;
begin
 init;
 nb;
 write(f2,f[s]);
 close(f1);close(f2);
end.